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

With no annotations provided, the description carries the full burden. It discloses that the tool computes and returns the key file URL, contents, and curl command, implying it does not itself fetch the file. It also adds a useful diagnostic heuristic about 403 errors. However, it does not explicitly state whether the operation is read-only or if any external calls are made, leaving a small gap.

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 two sentences with no fluff. The first sentence front-loads the primary purpose and outputs, while the second sentence adds a practical, non-essential troubleshooting tip. Every word earns its place; it is concise yet comprehensive.

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?

Without an output schema, the description clearly explains the return values (exact URL, contents, curl command). It also gives a real-world context with the 403 error note. It could be slightly more explicit about edge cases (e.g., behavior when host is omitted) but is generally complete for this tool's simplicity.

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?

The schema descriptions are minimal ('The key to check', 'Optional host... to compute the key file URL'), but the main description adds meaning by explaining the relationship between host and the computed key file URL. This goes beyond the schema alone, making the parameter purposes clearer.

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 function: 'Checks an IndexNow key against the protocol schema (length, character set)' and also describes the additional outputs (exact URL, contents, curl command). This specific verb+resource combination distinguishes it from sibling tools like build_indexnow_payload and diff_sitemaps.

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 provides clear context on when the tool is relevant, especially the 403 rejection troubleshooting hint: 'Most 403 rejections are a key file that returns an HTML 404 page with a 200 status.' While it implies usage (validating keys and getting verification steps), it does not explicitly name alternatives or state when not to use it, so it falls slightly short of a 5.

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