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

Annotations cover the safety profile (readOnly, idempotent, non-destructive), yet the description adds real behavioral context beyond them: it is free, needs no API key, runs no model, is an estimate that may differ from the post-hoc real charge, and errors on auto-routing ids. It also enumerates the returned fields, which matters because there is no output schema.

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?

Four tight sentences, front-loaded with what the tool does, then when to use it, then the return shape and the estimate caveat. The return-field list earns its place precisely because no output schema exists.

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 pure read-only estimation tool with no output schema, the description supplies everything an agent needs: purpose, timing, cost/free status, auth-free nature, return shape, precision caveat, and error condition.

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 all three parameters (model, prompt_tokens, completion_tokens) are already documented with units, minimums, and guidance on using max_tokens for a worst case. The description adds no parameter-level detail beyond the schema, so the baseline 3 applies.

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 precise verb+resource (estimate the cost of a chat completion on Synap) and the input basis (token counts, live price list). It is clearly distinguishable from synap_chat_completion, synap_list_models, and synap_get_model without opening any 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 explicit usage conditions: use before synap_chat_completion when budget matters, or to compare models for a job. It also names the failure case (auto-routing ids like synap-v1 have no fixed price and error out), which routes the agent correctly for the edge scenario.

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