diff --git a/include/secp256k1.h b/include/secp256k1.h
index 7be7fd5723..576953f49d 100644
--- a/include/secp256k1.h
+++ b/include/secp256k1.h
@@ -226,7 +226,7 @@ SECP256K1_API secp256k1_context* secp256k1_context_create(
  *  memory allocation entirely, see the functions in secp256k1_preallocated.h.
  *
  *  Returns: a newly created context object.
- *  Args:    ctx: an existing context to copy (cannot be NULL)
+ *  Args:    ctx: an existing context to copy
  */
 SECP256K1_API secp256k1_context* secp256k1_context_clone(
     const secp256k1_context* ctx
@@ -247,7 +247,7 @@ SECP256K1_API secp256k1_context* secp256k1_context_clone(
  */
 SECP256K1_API void secp256k1_context_destroy(
     secp256k1_context* ctx
-);
+) SECP256K1_ARG_NONNULL(1);
 
 /** Set a callback function to be called when an illegal argument is passed to
  *  an API call. It will only trigger for violations that are mentioned
@@ -278,11 +278,11 @@ SECP256K1_API void secp256k1_context_destroy(
  *  fails. In this case, the corresponding default handler will be called with
  *  the data pointer argument set to NULL.
  *
- *  Args: ctx:  an existing context object (cannot be NULL)
+ *  Args: ctx:  an existing context object.
  *  In:   fun:  a pointer to a function to call when an illegal argument is
  *              passed to the API, taking a message and an opaque pointer.
  *              (NULL restores the default handler.)
- *        data: the opaque pointer to pass to fun above.
+ *        data: the opaque pointer to pass to fun above, must be NULL for the default handler.
  *
  *  See also secp256k1_context_set_error_callback.
  */
@@ -302,12 +302,12 @@ SECP256K1_API void secp256k1_context_set_illegal_callback(
  *  for that). After this callback returns, anything may happen, including
  *  crashing.
  *
- *  Args: ctx:  an existing context object (cannot be NULL)
+ *  Args: ctx:  an existing context object.
  *  In:   fun:  a pointer to a function to call when an internal error occurs,
  *              taking a message and an opaque pointer (NULL restores the
  *              default handler, see secp256k1_context_set_illegal_callback
  *              for details).
- *        data: the opaque pointer to pass to fun above.
+ *        data: the opaque pointer to pass to fun above, must be NULL for the default handler.
  *
  *  See also secp256k1_context_set_illegal_callback.
  */
@@ -320,7 +320,7 @@ SECP256K1_API void secp256k1_context_set_error_callback(
 /** Create a secp256k1 scratch space object.
  *
  *  Returns: a newly created scratch space.
- *  Args: ctx:  an existing context object (cannot be NULL)
+ *  Args: ctx:  an existing context object.
  *  In:   size: amount of memory to be available as scratch space. Some extra
  *              (<100 bytes) will be allocated for extra accounting.
  */
@@ -480,8 +480,8 @@ SECP256K1_API int secp256k1_ecdsa_signature_serialize_compact(
  *  Returns: 1: correct signature
  *           0: incorrect or unparseable signature
  *  Args:    ctx:       a secp256k1 context object, initialized for verification.
- *  In:      sig:       the signature being verified (cannot be NULL)
- *           msghash32: the 32-byte message hash being verified (cannot be NULL).
+ *  In:      sig:       the signature being verified.
+ *           msghash32: the 32-byte message hash being verified.
  *                      The verifier must make sure to apply a cryptographic
  *                      hash function to the message by itself and not accept an
  *                      msghash32 value directly. Otherwise, it would be easy to
@@ -489,7 +489,7 @@ SECP256K1_API int secp256k1_ecdsa_signature_serialize_compact(
  *                      secret key. See also
  *                      https://bitcoin.stackexchange.com/a/81116/35586 for more
  *                      background on this topic.
- *           pubkey:    pointer to an initialized public key to verify with (cannot be NULL)
+ *           pubkey:    pointer to an initialized public key to verify with.
  *
  * To avoid accepting malleable signatures, only ECDSA signatures in lower-S
  * form are accepted.
@@ -515,8 +515,7 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdsa_verify(
  *                or copy if the input was already normalized. (can be NULL if
  *                you're only interested in whether the input was already
  *                normalized).
- *  In:   sigin:  a pointer to a signature to check/normalize (cannot be NULL,
- *                can be identical to sigout)
+ *  In:   sigin:  a pointer to a signature to check/normalize (can be identical to sigout)
  *
  *  With ECDSA a third-party can forge a second distinct signature of the same
  *  message, given a single initial signature, but without knowing the key. This
@@ -568,12 +567,16 @@ SECP256K1_API extern const secp256k1_nonce_function secp256k1_nonce_function_def
  *
  *  Returns: 1: signature created
  *           0: the nonce generation function failed, or the secret key was invalid.
- *  Args:    ctx:       pointer to a context object, initialized for signing (cannot be NULL)
- *  Out:     sig:       pointer to an array where the signature will be placed (cannot be NULL)
- *  In:      msghash32: the 32-byte message hash being signed (cannot be NULL)
- *           seckey:    pointer to a 32-byte secret key (cannot be NULL)
- *           noncefp:   pointer to a nonce generation function. If NULL, secp256k1_nonce_function_default is used
- *           ndata:     pointer to arbitrary data used by the nonce generation function (can be NULL)
+ *  Args:    ctx:       pointer to a context object, initialized for signing.
+ *  Out:     sig:       pointer to an array where the signature will be placed.
+ *  In:      msghash32: the 32-byte message hash being signed.
+ *           seckey:    pointer to a 32-byte secret key.
+ *           noncefp:   pointer to a nonce generation function. If NULL,
+ *                      secp256k1_nonce_function_default is used.
+ *           ndata:     pointer to arbitrary data used by the nonce generation function
+ *                      (can be NULL). If it is non-NULL and
+ *                      secp256k1_nonce_function_default is used, then ndata must be a
+ *                      pointer to 32-bytes of additional data.
  *
  * The created signature is always in lower-S form. See
  * secp256k1_ecdsa_signature_normalize for more details.
@@ -596,8 +599,8 @@ SECP256K1_API int secp256k1_ecdsa_sign(
  *
  *  Returns: 1: secret key is valid
  *           0: secret key is invalid
- *  Args:    ctx: pointer to a context object (cannot be NULL)
- *  In:      seckey: pointer to a 32-byte secret key (cannot be NULL)
+ *  Args:    ctx: pointer to a context object.
+ *  In:      seckey: pointer to a 32-byte secret key.
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_verify(
     const secp256k1_context* ctx,
@@ -606,11 +609,11 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_verify(
 
 /** Compute the public key for a secret key.
  *
- *  Returns: 1: secret was valid, public key stores
- *           0: secret was invalid, try again
- *  Args:   ctx:        pointer to a context object, initialized for signing (cannot be NULL)
- *  Out:    pubkey:     pointer to the created public key (cannot be NULL)
- *  In:     seckey:     pointer to a 32-byte secret key (cannot be NULL)
+ *  Returns: 1: secret was valid, public key stores.
+ *           0: secret was invalid, try again.
+ *  Args:    ctx:    pointer to a context object, initialized for signing.
+ *  Out:     pubkey: pointer to the created public key.
+ *  In:      seckey: pointer to a 32-byte secret key.
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_create(
     const secp256k1_context* ctx,
@@ -626,8 +629,7 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_create(
  *  In/Out: seckey: pointer to the 32-byte secret key to be negated. If the
  *                  secret key is invalid according to
  *                  secp256k1_ec_seckey_verify, this function returns 0 and
- *                  seckey will be set to some unspecified value. (cannot be
- *                  NULL)
+ *                  seckey will be set to some unspecified value.
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_negate(
     const secp256k1_context* ctx,
@@ -645,7 +647,7 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_negate(
  *
  *  Returns: 1 always
  *  Args:   ctx:        pointer to a context object
- *  In/Out: pubkey:     pointer to the public key to be negated (cannot be NULL)
+ *  In/Out: pubkey:     pointer to the public key to be negated.
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_negate(
     const secp256k1_context* ctx,
@@ -657,15 +659,15 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_negate(
  *  Returns: 0 if the arguments are invalid or the resulting secret key would be
  *           invalid (only when the tweak is the negation of the secret key). 1
  *           otherwise.
- *  Args:    ctx:   pointer to a context object (cannot be NULL).
+ *  Args:    ctx:   pointer to a context object.
  *  In/Out: seckey: pointer to a 32-byte secret key. If the secret key is
  *                  invalid according to secp256k1_ec_seckey_verify, this
  *                  function returns 0. seckey will be set to some unspecified
- *                  value if this function returns 0. (cannot be NULL)
+ *                  value if this function returns 0.
  *  In:    tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
  *                  secp256k1_ec_seckey_verify, this function returns 0. For
  *                  uniformly random 32-byte arrays the chance of being invalid
- *                  is negligible (around 1 in 2^128) (cannot be NULL).
+ *                  is negligible (around 1 in 2^128).
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_tweak_add(
     const secp256k1_context* ctx,
@@ -686,14 +688,13 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_tweak_add(
  *  Returns: 0 if the arguments are invalid or the resulting public key would be
  *           invalid (only when the tweak is the negation of the corresponding
  *           secret key). 1 otherwise.
- *  Args:    ctx:   pointer to a context object initialized for validation
- *                  (cannot be NULL).
+ *  Args:    ctx:   pointer to a context object initialized for validation.
  *  In/Out: pubkey: pointer to a public key object. pubkey will be set to an
- *                  invalid value if this function returns 0 (cannot be NULL).
+ *                  invalid value if this function returns 0.
  *  In:    tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
  *                  secp256k1_ec_seckey_verify, this function returns 0. For
  *                  uniformly random 32-byte arrays the chance of being invalid
- *                  is negligible (around 1 in 2^128) (cannot be NULL).
+ *                  is negligible (around 1 in 2^128).
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_add(
     const secp256k1_context* ctx,
@@ -704,15 +705,15 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_add(
 /** Tweak a secret key by multiplying it by a tweak.
  *
  *  Returns: 0 if the arguments are invalid. 1 otherwise.
- *  Args:   ctx:    pointer to a context object (cannot be NULL).
+ *  Args:   ctx:    pointer to a context object.
  *  In/Out: seckey: pointer to a 32-byte secret key. If the secret key is
  *                  invalid according to secp256k1_ec_seckey_verify, this
  *                  function returns 0. seckey will be set to some unspecified
- *                  value if this function returns 0. (cannot be NULL)
+ *                  value if this function returns 0.
  *  In:    tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
  *                  secp256k1_ec_seckey_verify, this function returns 0. For
  *                  uniformly random 32-byte arrays the chance of being invalid
- *                  is negligible (around 1 in 2^128) (cannot be NULL).
+ *                  is negligible (around 1 in 2^128).
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_seckey_tweak_mul(
     const secp256k1_context* ctx,
@@ -731,14 +732,13 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_tweak_mul(
 /** Tweak a public key by multiplying it by a tweak value.
  *
  *  Returns: 0 if the arguments are invalid. 1 otherwise.
- *  Args:    ctx:   pointer to a context object initialized for validation
- *                  (cannot be NULL).
+ *  Args:    ctx:   pointer to a context object initialized for validation.
  *  In/Out: pubkey: pointer to a public key object. pubkey will be set to an
- *                  invalid value if this function returns 0 (cannot be NULL).
+ *                  invalid value if this function returns 0.
  *  In:    tweak32: pointer to a 32-byte tweak. If the tweak is invalid according to
  *                  secp256k1_ec_seckey_verify, this function returns 0. For
  *                  uniformly random 32-byte arrays the chance of being invalid
- *                  is negligible (around 1 in 2^128) (cannot be NULL).
+ *                  is negligible (around 1 in 2^128).
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_mul(
     const secp256k1_context* ctx,
@@ -749,7 +749,7 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_tweak_mul(
 /** Updates the context randomization to protect against side-channel leakage.
  *  Returns: 1: randomization successfully updated or nothing to randomize
  *           0: error
- *  Args:    ctx:       pointer to a context object (cannot be NULL)
+ *  Args:    ctx:       pointer to a context object.
  *  In:      seed32:    pointer to a 32-byte random seed (NULL resets to initial state)
  *
  * While secp256k1 code is written to be constant-time no matter what secret
@@ -780,18 +780,17 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_context_randomize(
  *
  *  Returns: 1: the sum of the public keys is valid.
  *           0: the sum of the public keys is not valid.
- *  Args:   ctx:        pointer to a context object
- *  Out:    out:        pointer to a public key object for placing the resulting public key
- *                      (cannot be NULL)
- *  In:     ins:        pointer to array of pointers to public keys (cannot be NULL)
- *          n:          the number of public keys to add together (must be at least 1)
+ *  Args:   ctx:        pointer to a context object.
+ *  Out:    out:        pointer to a public key object for placing the resulting public key.
+ *  In:     ins:        pointer to array of pointers to public keys.
+ *          n:          the number of public keys to add together (must be at least 1).
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_pubkey_combine(
     const secp256k1_context* ctx,
     secp256k1_pubkey *out,
     const secp256k1_pubkey * const * ins,
     size_t n
-) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
+) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
 
 /** Compute a tagged hash as defined in BIP-340.
  *
diff --git a/include/secp256k1_ecdh.h b/include/secp256k1_ecdh.h
index 4058e9c043..c8577984b1 100644
--- a/include/secp256k1_ecdh.h
+++ b/include/secp256k1_ecdh.h
@@ -37,14 +37,15 @@ SECP256K1_API extern const secp256k1_ecdh_hash_function secp256k1_ecdh_hash_func
  *
  *  Returns: 1: exponentiation was successful
  *           0: scalar was invalid (zero or overflow) or hashfp returned 0
- *  Args:    ctx:        pointer to a context object (cannot be NULL)
- *  Out:     output:     pointer to an array to be filled by hashfp
- *  In:      pubkey:     a pointer to a secp256k1_pubkey containing an
- *                       initialized public key
- *           seckey:     a 32-byte scalar with which to multiply the point
- *           hashfp:     pointer to a hash function. If NULL, secp256k1_ecdh_hash_function_sha256 is used
- *                       (in which case, 32 bytes will be written to output)
+ *  Args:    ctx:        pointer to a context object.
+ *  Out:     output:     pointer to an array to be filled by hashfp.
+ *  In:      pubkey:     a pointer to a secp256k1_pubkey containing an initialized public key.
+ *           seckey:     a 32-byte scalar with which to multiply the point.
+ *           hashfp:     pointer to a hash function. If NULL,
+ *                       secp256k1_ecdh_hash_function_sha256 is used
+ *                       (in which case, 32 bytes will be written to output).
  *           data:       arbitrary data pointer that is passed through to hashfp
+ *                       (can be NULL for secp256k1_ecdh_hash_function_sha256).
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdh(
   const secp256k1_context* ctx,
diff --git a/include/secp256k1_extrakeys.h b/include/secp256k1_extrakeys.h
index 0a37fb6b9d..a64d561b60 100644
--- a/include/secp256k1_extrakeys.h
+++ b/include/secp256k1_extrakeys.h
@@ -39,11 +39,10 @@ typedef struct {
  *  Returns: 1 if the public key was fully valid.
  *           0 if the public key could not be parsed or is invalid.
  *
- *  Args:   ctx: a secp256k1 context object (cannot be NULL).
+ *  Args:   ctx: a secp256k1 context object.
  *  Out: pubkey: pointer to a pubkey object. If 1 is returned, it is set to a
  *               parsed version of input. If not, it's set to an invalid value.
- *               (cannot be NULL).
- *  In: input32: pointer to a serialized xonly_pubkey (cannot be NULL)
+ *  In: input32: pointer to a serialized xonly_pubkey.
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_xonly_pubkey_parse(
     const secp256k1_context* ctx,
@@ -55,11 +54,9 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_xonly_pubkey_parse(
  *
  *  Returns: 1 always.
  *
- *  Args:     ctx: a secp256k1 context object (cannot be NULL).
- *  Out: output32: a pointer to a 32-byte array to place the serialized key in
- *                 (cannot be NULL).
- *  In:    pubkey: a pointer to a secp256k1_xonly_pubkey containing an
- *                 initialized public key (cannot be NULL).
+ *  Args:     ctx: a secp256k1 context object.
+ *  Out: output32: a pointer to a 32-byte array to place the serialized key in.
+ *  In:    pubkey: a pointer to a secp256k1_xonly_pubkey containing an initialized public key.
  */
 SECP256K1_API int secp256k1_xonly_pubkey_serialize(
     const secp256k1_context* ctx,
@@ -87,13 +84,12 @@ SECP256K1_API int secp256k1_xonly_pubkey_cmp(
  *  Returns: 1 if the public key was successfully converted
  *           0 otherwise
  *
- *  Args:         ctx: pointer to a context object (cannot be NULL)
- *  Out: xonly_pubkey: pointer to an x-only public key object for placing the
- *                     converted public key (cannot be NULL)
- *          pk_parity: pointer to an integer that will be set to 1 if the point
- *                     encoded by xonly_pubkey is the negation of the pubkey and
- *                     set to 0 otherwise. (can be NULL)
- *  In:        pubkey: pointer to a public key that is converted (cannot be NULL)
+ *  Args:         ctx: pointer to a context object.
+ *  Out: xonly_pubkey: pointer to an x-only public key object for placing the converted public key.
+ *          pk_parity: Ignored if NULL. Otherwise, pointer to an integer that
+ *                     will be set to 1 if the point encoded by xonly_pubkey is
+ *                     the negation of the pubkey and set to 0 otherwise.
+ *  In:        pubkey: pointer to a public key that is converted.
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_xonly_pubkey_from_pubkey(
     const secp256k1_context* ctx,
@@ -113,18 +109,14 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_xonly_pubkey_from_pubke
  *           invalid (only when the tweak is the negation of the corresponding
  *           secret key). 1 otherwise.
  *
- *  Args:           ctx: pointer to a context object initialized for verification
- *                       (cannot be NULL)
+ *  Args:           ctx: pointer to a context object initialized for verification.
  *  Out:  output_pubkey: pointer to a public key to store the result. Will be set
- *                       to an invalid value if this function returns 0 (cannot
- *                       be NULL)
+ *                       to an invalid value if this function returns 0.
  *  In: internal_pubkey: pointer to an x-only pubkey to apply the tweak to.
- *                       (cannot be NULL).
  *              tweak32: pointer to a 32-byte tweak. If the tweak is invalid
  *                       according to secp256k1_ec_seckey_verify, this function
  *                       returns 0. For uniformly random 32-byte arrays the
- *                       chance of being invalid is negligible (around 1 in
- *                       2^128) (cannot be NULL).
+ *                       chance of being invalid is negligible (around 1 in 2^128).
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_xonly_pubkey_tweak_add(
     const secp256k1_context* ctx,
@@ -146,17 +138,15 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_xonly_pubkey_tweak_add(
  *
  *  Returns: 0 if the arguments are invalid or the tweaked pubkey is not the
  *           result of tweaking the internal_pubkey with tweak32. 1 otherwise.
- *  Args:            ctx: pointer to a context object initialized for verification
- *                       (cannot be NULL)
- *  In: tweaked_pubkey32: pointer to a serialized xonly_pubkey (cannot be NULL)
+ *  Args:            ctx: pointer to a context object initialized for verification.
+ *  In: tweaked_pubkey32: pointer to a serialized xonly_pubkey.
  *     tweaked_pk_parity: the parity of the tweaked pubkey (whose serialization
  *                        is passed in as tweaked_pubkey32). This must match the
  *                        pk_parity value that is returned when calling
  *                        secp256k1_xonly_pubkey with the tweaked pubkey, or
  *                        this function will fail.
- *       internal_pubkey: pointer to an x-only public key object to apply the
- *                        tweak to (cannot be NULL)
- *               tweak32: pointer to a 32-byte tweak (cannot be NULL)
+ *       internal_pubkey: pointer to an x-only public key object to apply the tweak to.
+ *               tweak32: pointer to a 32-byte tweak.
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_xonly_pubkey_tweak_add_check(
     const secp256k1_context* ctx,
@@ -170,9 +160,9 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_xonly_pubkey_tweak_add_
  *
  *  Returns: 1: secret was valid, keypair is ready to use
  *           0: secret was invalid, try again with a different secret
- *  Args:    ctx: pointer to a context object, initialized for signing (cannot be NULL)
- *  Out: keypair: pointer to the created keypair (cannot be NULL)
- *  In:   seckey: pointer to a 32-byte secret key (cannot be NULL)
+ *  Args:    ctx: pointer to a context object, initialized for signing.
+ *  Out: keypair: pointer to the created keypair.
+ *  In:   seckey: pointer to a 32-byte secret key.
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_keypair_create(
     const secp256k1_context* ctx,
@@ -183,9 +173,9 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_keypair_create(
 /** Get the secret key from a keypair.
  *
  *  Returns: 0 if the arguments are invalid. 1 otherwise.
- *  Args:   ctx: pointer to a context object (cannot be NULL)
- *  Out: seckey: pointer to a 32-byte buffer for the secret key (cannot be NULL)
- *  In: keypair: pointer to a keypair (cannot be NULL)
+ *  Args:   ctx: pointer to a context object.
+ *  Out: seckey: pointer to a 32-byte buffer for the secret key.
+ *  In: keypair: pointer to a keypair.
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_keypair_sec(
     const secp256k1_context* ctx,
@@ -196,11 +186,10 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_keypair_sec(
 /** Get the public key from a keypair.
  *
  *  Returns: 0 if the arguments are invalid. 1 otherwise.
- *  Args:    ctx: pointer to a context object (cannot be NULL)
+ *  Args:    ctx: pointer to a context object.
  *  Out: pubkey: pointer to a pubkey object. If 1 is returned, it is set to
  *               the keypair public key. If not, it's set to an invalid value.
- *               (cannot be NULL)
- *  In: keypair: pointer to a keypair (cannot be NULL)
+ *  In: keypair: pointer to a keypair.
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_keypair_pub(
     const secp256k1_context* ctx,
@@ -214,14 +203,13 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_keypair_pub(
  *  secp256k1_xonly_pubkey_from_pubkey.
  *
  *  Returns: 0 if the arguments are invalid. 1 otherwise.
- *  Args:   ctx: pointer to a context object (cannot be NULL)
+ *  Args:   ctx: pointer to a context object.
  *  Out: pubkey: pointer to an xonly_pubkey object. If 1 is returned, it is set
  *               to the keypair public key after converting it to an
- *               xonly_pubkey. If not, it's set to an invalid value (cannot be
- *               NULL).
- *    pk_parity: pointer to an integer that will be set to the pk_parity
- *               argument of secp256k1_xonly_pubkey_from_pubkey (can be NULL).
- *  In: keypair: pointer to a keypair (cannot be NULL)
+ *               xonly_pubkey. If not, it's set to an invalid value.
+ *    pk_parity: Ignored if NULL. Otherwise, pointer to an integer that will be set to the
+ *               pk_parity argument of secp256k1_xonly_pubkey_from_pubkey.
+ *  In: keypair: pointer to a keypair.
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_keypair_xonly_pub(
     const secp256k1_context* ctx,
@@ -241,15 +229,13 @@ SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_keypair_xonly_pub(
  *           invalid (only when the tweak is the negation of the keypair's
  *           secret key). 1 otherwise.
  *
- *  Args:       ctx: pointer to a context object initialized for verification
- *                   (cannot be NULL)
+ *  Args:       ctx: pointer to a context object initialized for verification.
  *  In/Out: keypair: pointer to a keypair to apply the tweak to. Will be set to
- *                   an invalid value if this function returns 0 (cannot be
- *                   NULL).
+ *                   an invalid value if this function returns 0.
  *  In:     tweak32: pointer to a 32-byte tweak. If the tweak is invalid according
  *                   to secp256k1_ec_seckey_verify, this function returns 0. For
  *                   uniformly random 32-byte arrays the chance of being invalid
- *                   is negligible (around 1 in 2^128) (cannot be NULL).
+ *                   is negligible (around 1 in 2^128).
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_keypair_xonly_tweak_add(
     const secp256k1_context* ctx,
diff --git a/include/secp256k1_preallocated.h b/include/secp256k1_preallocated.h
index a9ae15d5ae..d2d9014f02 100644
--- a/include/secp256k1_preallocated.h
+++ b/include/secp256k1_preallocated.h
@@ -55,7 +55,7 @@ SECP256K1_API size_t secp256k1_context_preallocated_size(
  *  Returns: a newly created context object.
  *  In:      prealloc: a pointer to a rewritable contiguous block of memory of
  *                     size at least secp256k1_context_preallocated_size(flags)
- *                     bytes, as detailed above (cannot be NULL)
+ *                     bytes, as detailed above.
  *           flags:    which parts of the context to initialize.
  *
  *  See also secp256k1_context_randomize (in secp256k1.h)
@@ -70,7 +70,7 @@ SECP256K1_API secp256k1_context* secp256k1_context_preallocated_create(
  *  caller-provided memory.
  *
  *  Returns: the required size of the caller-provided memory block.
- *  In:      ctx: an existing context to copy (cannot be NULL)
+ *  In:      ctx: an existing context to copy.
  */
 SECP256K1_API size_t secp256k1_context_preallocated_clone_size(
     const secp256k1_context* ctx
@@ -87,10 +87,10 @@ SECP256K1_API size_t secp256k1_context_preallocated_clone_size(
  *  secp256k1_context_preallocated_create for details.
  *
  *  Returns: a newly created context object.
- *  Args:    ctx:      an existing context to copy (cannot be NULL)
+ *  Args:    ctx:      an existing context to copy.
  *  In:      prealloc: a pointer to a rewritable contiguous block of memory of
  *                     size at least secp256k1_context_preallocated_size(flags)
- *                     bytes, as detailed above (cannot be NULL)
+ *                     bytes, as detailed above.
  */
 SECP256K1_API secp256k1_context* secp256k1_context_preallocated_clone(
     const secp256k1_context* ctx,
@@ -115,11 +115,11 @@ SECP256K1_API secp256k1_context* secp256k1_context_preallocated_clone(
  *
  *  Args:   ctx: an existing context to destroy, constructed using
  *               secp256k1_context_preallocated_create or
- *               secp256k1_context_preallocated_clone (cannot be NULL)
+ *               secp256k1_context_preallocated_clone.
  */
 SECP256K1_API void secp256k1_context_preallocated_destroy(
     secp256k1_context* ctx
-);
+) SECP256K1_ARG_NONNULL(1);
 
 #ifdef __cplusplus
 }
diff --git a/include/secp256k1_recovery.h b/include/secp256k1_recovery.h
index aa16532ce8..0e2847db96 100644
--- a/include/secp256k1_recovery.h
+++ b/include/secp256k1_recovery.h
@@ -43,8 +43,9 @@ SECP256K1_API int secp256k1_ecdsa_recoverable_signature_parse_compact(
 /** Convert a recoverable signature into a normal signature.
  *
  *  Returns: 1
- *  Out: sig:    a pointer to a normal signature (cannot be NULL).
- *  In:  sigin:  a pointer to a recoverable signature (cannot be NULL).
+ *  Args: ctx:    a secp256k1 context object.
+ *  Out:  sig:    a pointer to a normal signature.
+ *  In:   sigin:  a pointer to a recoverable signature.
  */
 SECP256K1_API int secp256k1_ecdsa_recoverable_signature_convert(
     const secp256k1_context* ctx,
@@ -55,10 +56,10 @@ SECP256K1_API int secp256k1_ecdsa_recoverable_signature_convert(
 /** Serialize an ECDSA signature in compact format (64 bytes + recovery id).
  *
  *  Returns: 1
- *  Args: ctx:      a secp256k1 context object
- *  Out:  output64: a pointer to a 64-byte array of the compact signature (cannot be NULL)
- *        recid:    a pointer to an integer to hold the recovery id (can be NULL).
- *  In:   sig:      a pointer to an initialized signature object (cannot be NULL)
+ *  Args: ctx:      a secp256k1 context object.
+ *  Out:  output64: a pointer to a 64-byte array of the compact signature.
+ *        recid:    a pointer to an integer to hold the recovery id.
+ *  In:   sig:      a pointer to an initialized signature object.
  */
 SECP256K1_API int secp256k1_ecdsa_recoverable_signature_serialize_compact(
     const secp256k1_context* ctx,
@@ -71,12 +72,14 @@ SECP256K1_API int secp256k1_ecdsa_recoverable_signature_serialize_compact(
  *
  *  Returns: 1: signature created
  *           0: the nonce generation function failed, or the secret key was invalid.
- *  Args:    ctx:       pointer to a context object, initialized for signing (cannot be NULL)
- *  Out:     sig:       pointer to an array where the signature will be placed (cannot be NULL)
- *  In:      msghash32: the 32-byte message hash being signed (cannot be NULL)
- *           seckey:    pointer to a 32-byte secret key (cannot be NULL)
- *           noncefp:   pointer to a nonce generation function. If NULL, secp256k1_nonce_function_default is used
- *           ndata:     pointer to arbitrary data used by the nonce generation function (can be NULL)
+ *  Args:    ctx:       pointer to a context object, initialized for signing.
+ *  Out:     sig:       pointer to an array where the signature will be placed.
+ *  In:      msghash32: the 32-byte message hash being signed.
+ *           seckey:    pointer to a 32-byte secret key.
+ *           noncefp:   pointer to a nonce generation function. If NULL,
+ *                      secp256k1_nonce_function_default is used.
+ *           ndata:     pointer to arbitrary data used by the nonce generation function
+ *                      (can be NULL for secp256k1_nonce_function_default).
  */
 SECP256K1_API int secp256k1_ecdsa_sign_recoverable(
     const secp256k1_context* ctx,
@@ -91,10 +94,10 @@ SECP256K1_API int secp256k1_ecdsa_sign_recoverable(
  *
  *  Returns: 1: public key successfully recovered (which guarantees a correct signature).
  *           0: otherwise.
- *  Args:    ctx:       pointer to a context object, initialized for verification (cannot be NULL)
- *  Out:     pubkey:    pointer to the recovered public key (cannot be NULL)
- *  In:      sig:       pointer to initialized signature that supports pubkey recovery (cannot be NULL)
- *           msghash32: the 32-byte message hash assumed to be signed (cannot be NULL)
+ *  Args:    ctx:       pointer to a context object, initialized for verification.
+ *  Out:     pubkey:    pointer to the recovered public key.
+ *  In:      sig:       pointer to initialized signature that supports pubkey recovery.
+ *           msghash32: the 32-byte message hash assumed to be signed.
  */
 SECP256K1_API SECP256K1_WARN_UNUSED_RESULT int secp256k1_ecdsa_recover(
     const secp256k1_context* ctx,
diff --git a/include/secp256k1_schnorrsig.h b/include/secp256k1_schnorrsig.h
index d68bba62cc..c42cb10f2b 100644
--- a/include/secp256k1_schnorrsig.h
+++ b/include/secp256k1_schnorrsig.h
@@ -106,10 +106,10 @@ typedef struct {
  *  signatures from being valid in multiple contexts by accident.
  *
  *  Returns 1 on success, 0 on failure.
- *  Args:    ctx: pointer to a context object, initialized for signing (cannot be NULL)
- *  Out:   sig64: pointer to a 64-byte array to store the serialized signature (cannot be NULL)
- *  In:    msg32: the 32-byte message being signed (cannot be NULL)
- *       keypair: pointer to an initialized keypair (cannot be NULL)
+ *  Args:    ctx: pointer to a context object, initialized for signing.
+ *  Out:   sig64: pointer to a 64-byte array to store the serialized signature.
+ *  In:    msg32: the 32-byte message being signed.
+ *       keypair: pointer to an initialized keypair.
  *    aux_rand32: 32 bytes of fresh randomness. While recommended to provide
  *                this, it is only supplemental to security and can be NULL. See
  *                BIP-340 "Default Signing" for a full explanation of this
@@ -150,7 +150,7 @@ SECP256K1_API int secp256k1_schnorrsig_sign_custom(
  *  Returns: 1: correct signature
  *           0: incorrect signature
  *  Args:    ctx: a secp256k1 context object, initialized for verification.
- *  In:    sig64: pointer to the 64-byte signature to verify (cannot be NULL)
+ *  In:    sig64: pointer to the 64-byte signature to verify.
  *           msg: the message being verified. Can only be NULL if msglen is 0.
  *        msglen: length of the message
  *        pubkey: pointer to an x-only public key to verify with (cannot be NULL)
diff --git a/src/modules/recovery/main_impl.h b/src/modules/recovery/main_impl.h
index 9e19f2a2dc..3f29570198 100644
--- a/src/modules/recovery/main_impl.h
+++ b/src/modules/recovery/main_impl.h
@@ -40,7 +40,7 @@ int secp256k1_ecdsa_recoverable_signature_parse_compact(const secp256k1_context*
     int ret = 1;
     int overflow = 0;
 
-    (void)ctx;
+    VERIFY_CHECK(ctx != NULL);
     ARG_CHECK(sig != NULL);
     ARG_CHECK(input64 != NULL);
     ARG_CHECK(recid >= 0 && recid <= 3);
@@ -60,7 +60,7 @@ int secp256k1_ecdsa_recoverable_signature_parse_compact(const secp256k1_context*
 int secp256k1_ecdsa_recoverable_signature_serialize_compact(const secp256k1_context* ctx, unsigned char *output64, int *recid, const secp256k1_ecdsa_recoverable_signature* sig) {
     secp256k1_scalar r, s;
 
-    (void)ctx;
+    VERIFY_CHECK(ctx != NULL);
     ARG_CHECK(output64 != NULL);
     ARG_CHECK(sig != NULL);
     ARG_CHECK(recid != NULL);
@@ -75,7 +75,7 @@ int secp256k1_ecdsa_recoverable_signature_convert(const secp256k1_context* ctx,
     secp256k1_scalar r, s;
     int recid;
 
-    (void)ctx;
+    VERIFY_CHECK(ctx != NULL);
     ARG_CHECK(sig != NULL);
     ARG_CHECK(sigin != NULL);
 
diff --git a/src/secp256k1.c b/src/secp256k1.c
index 9908cab864..adff3ae1be 100644
--- a/src/secp256k1.c
+++ b/src/secp256k1.c
@@ -771,6 +771,7 @@ int secp256k1_ec_pubkey_combine(const secp256k1_context* ctx, secp256k1_pubkey *
     secp256k1_gej Qj;
     secp256k1_ge Q;
 
+    VERIFY_CHECK(ctx != NULL);
     ARG_CHECK(pubnonce != NULL);
     memset(pubnonce, 0, sizeof(*pubnonce));
     ARG_CHECK(n >= 1);
@@ -779,6 +780,7 @@ int secp256k1_ec_pubkey_combine(const secp256k1_context* ctx, secp256k1_pubkey *
     secp256k1_gej_set_infinity(&Qj);
 
     for (i = 0; i < n; i++) {
+        ARG_CHECK(pubnonces[i] != NULL);
         secp256k1_pubkey_load(ctx, &Q, pubnonces[i]);
         secp256k1_gej_add_ge(&Qj, &Qj, &Q);
     }