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

Annotations only declare readOnlyHint=false, so the description carries the rest of the burden. It adds genuinely useful context (no cost, no pass required), but says nothing about permissions, moderation, posting limits, or whether the post is editable/deletable afterward — notable gaps for a mutation tool.

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?

Three short, front-loaded sentences with no filler. The core action is stated first, then cost context, then parameter mapping — every sentence 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?

For a 3-parameter write tool with 100% schema coverage and no output schema, the description is nearly sufficient. It covers the action, the cost model, and both optional parameters, though it omits validation constraints (e.g., whether reply_to must reference an existing post, length enforcement).

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 schema already documents all three parameters (char limits, topic id source, post_id meaning). The description restates the effect of `topic` and `reply_to` in plain terms, adding only marginal clarity beyond the schema — the baseline 3 is appropriate.

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?

States a specific verb and resource ('Write a post'), so the agent knows exactly what action occurs. It does not explicitly differentiate from nearby siblings like project100_feed or project100_topics, but no sibling performs the same write, so ambiguity is low.

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 'Free — there is nothing to pay and no pass to hold' clause is useful routing context that distinguishes this from the paid siblings (coin_send, market_order, seal, etc.). However, it gives no explicit when-to-use vs when-not-to-use guidance or prerequisites, so usage is implied rather than stated.

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