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

With no annotations, the description carries the behavioral burden. It discloses that this is an authenticated read operation over all letters for a key, but it does not say whether reading consumes letters, what failure modes exist, or what the response contains. 'Read' implies no side effects, yet the auth step and lack of return-value detail leave gaps.

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?

Two short sentences with no filler and the primary action is front-loaded. However, 'Sign the nonce' is an imperative usage note that could have been more explicit, though it still earns its place.

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?

There is no output schema and no annotations, so the description should explain what the agent gets back and any prerequisites. It does not describe the response format, whether all letters are returned at once, or that the nonce must first be obtained from letter_challenge; that last point is only recoverable from the schema's nonce description.

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 description coverage is 100%, so the baseline is 3. The description adds little beyond the schema: 'this key' maps to pubkey and 'Sign the nonce' restates the signature's purpose already described in the signature parameter.

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 uses a specific verb ('Read'), names the resource ('every letter left'), and identifies the scope ('this key'). This clearly distinguishes it from siblings like letter_write and letter_challenge, which are about writing letters or issuing a challenge.

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 instruction 'Sign the nonce' implies that the caller must first obtain a nonce from letter_challenge, but the tool description never explicitly states this prerequisite or contrasts letter_read with its siblings. Usage context is only implied, not spelled out.

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