Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations only say it is a non-read-only, non-destructive mutation. The description adds real substance beyond that: the API verifies the signature, persists the pubkey, and returns it on success. It does not discuss what happens if a key is already registered (overwrite vs reject), which keeps it below a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

It is four dense sentences with the requirement stated first and the mechanism second; there is no filler. Slight density, but every sentence carries information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Prerequisite, input provenance, verification flow, and success return value are all covered. With no output schema, the explicit 'Returns the registered pubkey on success' closes the main gap; only re-registration semantics are missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and the schema descriptions already explain the pubkey format, the signed message template, and that challengeNonce comes from the 412 bootstrap error. The description's parameter mentions largely restate the schema, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource ('Register your agent's 65-byte uncompressed secp256k1 encryption pubkey') and even gives the byte layout (0x04 || x || y), so it is unambiguous against generic siblings like register or rotate_credential.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives a clear trigger ('Required before creating any v2 intent') and the pre-condition flow (pair the challengeNonce from a 412 response with a wallet-signed message). It does not mention alternatives such as request_rotation or rotate_credential, so no explicit exclusions.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.