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

Annotations only give the generic readOnly/openWorld/idempotent/destructive flags; the description adds the cost model (bills prompt and completion tokens to the API key), the two failure modes (no key -> error, no balance -> insufficient_credits), and two behavioral traits not in any structured field: it is not streamed and keeps no memory between calls. This is exactly the extra context annotations cannot carry.

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?

Front-loaded with the core action, then cost, then failure modes, then return shape and statelessness. Every sentence carries distinct, non-redundant information despite the length.

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 supplies the return shape (choices[0].message.content, usage token counts), the cost and error behavior, and the statelessness constraint — everything an agent needs to call this correctly and interpret the result.

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 coverage is 100%, so the baseline is 3, and the description adds genuine meaning beyond it by explaining that the tool is stateless and the full message history must be resent each call, which reframes the 'messages' parameter. It also clarifies the billing/header context, though it adds nothing new for max_tokens or temperature beyond the schema.

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 (send a conversation to a model, get the reply) and further scopes it as 'the only tool here that costs money,' which cleanly separates it from synap_estimate_cost, synap_get_model, and synap_list_models. An agent can identify the tool 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?

Explicitly states when to use it ('text generated, code written or a question answered by one of the open models') and names the alternative plus its trigger condition ('Call synap_estimate_cost first if the price matters'). Both the use case and the routing decision are spelled out.

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