X official API read

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

Goes well past the annotations with operationally critical detail: auth is X_BEARER_TOKEN, X bills each read and the receipt carries a cost estimate, per-host pacing with backoff on 429/503, a single User-Agent, no login, no cookies. That is exactly the kind of cost/rate-limit/auth context that annotations (readOnlyHint, openWorldHint) cannot convey.

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 dense sentences, front-loaded with the 'Use when...' trigger and then the cost/network profile. No filler, though the auth/cost/network sentence is packed and slightly long relative to the rest.

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?

With no output schema, the description carries the return burden and does state 'Returns JSON and a receipt,' plus auth, billing, and network behavior. It is complete enough to call correctly, with only the receipt/JSON shape left unspecified.

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 80%, so the schema already documents id/query/username/max. The description adds semantic meaning by unpacking the three enum values (post, search_recent, user_posts) into plain-language operations, telling the agent what each op actually does beyond the bare enum tokens.

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?

Names a specific resource (X posts/user posts), a specific retrieval mode (post lookup, recent search, user's recent posts), and the provider (official X API v2). The 'official X API v2' scoping implicitly separates it from the sibling telos.x.oembed, so an agent can route without opening either 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?

Gives a clear activation condition (user has an X developer key) plus the three intended use cases, which map directly to the op enum. It stops short of explicitly naming the oembed sibling as the alternative when a developer key is unavailable, so the exclusion is only implied.

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