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

With no annotations, the description carries the full burden of disclosure. It is transparent about the algorithm (ECDH+HKDF), output fields (derived_key_in_hex and derived_key_length), and limitations (Ed25519 not usable, X25519 usable). It also notes optional salt/info and password handling. It does not discuss error cases, but for a crypto tool this level of transparency is solid.

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?

The description is well-structured with a clear breakdown of parameters, output, and limitations. It is slightly verbose but every section earns its place, and the front-loaded purpose statement makes it easy to scan. The use of bullet-like formatting enhances readability without unnecessary fluff.

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?

Given the tool's complexity (7 parameters) and lack of an output schema, the description covers the essential aspects: algorithm, parameter purposes, output format, and curve restrictions. It falls short of explicitly marking required parameters and handling edge cases, but overall it is sufficiently complete for an agent to invoke the tool correctly.

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%, so the baseline is 3. The description adds meaningful clarity beyond the schema by explaining roles (own private key vs. other's public key), the condition for the password, and the valid range for derived_key_length. It also explicitly calls out unsupported Sm3, which is useful. This additional context justifies the higher score.

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 clearly states the tool's purpose: ECDH + HKDF key negotiation, where both parties derive the same symmetric key using their own private key and the other's public key. This specific verb+resource combination distinguishes it from sibling tools like hybrid_kex and ecc_key_sign, making its function unambiguous.

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?

The description gives clear context: both parties need their own private key and the other's public key, and the output is a derived symmetric key. It also provides exclusions such as Ed25519 not available and Sm3 not supported, plus a conditional for encrypted private keys. However, it does not explicitly mention alternatives like hybrid_kex, so it stops short of a perfect 5.

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