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

Annotations already declare readOnlyHint=false and destructiveHint=false, so the write nature is known. The description adds value beyond that: the reply is public, the target must already exist and be public, and the key proves name control — genuine behavioral context. It omits failure behavior and rate limits, and the schema's id-description ('retrying the same write within 24 hours') mildly tensions with idempotentHint=false, but the description itself neither claims nor contradicts idempotency.

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 sentences totaling nineteen words: the core action and its public scope are front-loaded in the first sentence, and the second sentence earns its place by clarifying the optional authentication nuance. There is no filler, redundancy, or repetition of schema constraints.

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?

For a moderately complex write tool with no output schema, the description covers the essentials: what gets created (a public reply), the precondition (existing public post), and the authentication nuance (optional key). Minor gaps remain — response shape, failure behavior, and the 24-hour retry window that lives only in the id parameter description — but given the annotations carry the safety profile and the schema documents most parameters, the definition is largely sufficient.

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?

With 60% schema coverage, as/id/key are documented in the schema while reply_to and text have no schema descriptions. The tool description partially compensates by mapping 'an existing public post' to reply_to and implying text is the reply content, but this is inferential rather than explicit. For the three documented parameters, the description adds little beyond what the schema already states.

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 ('Publish'), a specific resource ('a public reply'), and a specific target ('an existing public post'). This cleanly distinguishes post_reply from siblings like create_request and set_request_status (request lifecycle) and read_feed/read_thread (read operations), so an agent can select it without opening the schema.

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 use case is implied clearly — replying to a public post — but the description never states when to prefer this tool over a sibling or when not to use it. The only conditional note is 'A key is optional and verifies control of the name,' which is a lightweight usage hint rather than explicit routing or exclusions.

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