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

With no annotations, the description carries the full burden and does so well: it discloses the x402 payment model ($0.01 USDC on Base), that charging only occurs on a 200, and the failure semantics (404 unknown id, 400 invalid args, 503 during refresh). These are exactly the operational facts an agent needs before invoking a paid endpoint.

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 important facts are front-loaded and the description is short, but it repeats itself: id provenance is stated twice ('comes from the free /api/v1/opportunities' and 'ids come from search_opportunities'), as is the 'charged only for a 200 / successful answer' point. Two sentences could be merged or dropped.

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 2-parameter tool with no annotations and no output schema, the description covers purpose, price, error codes, and id provenance. The remaining gap is the return shape (array length, whether points are sorted or sparse), which the agent must infer from 'daily history'.

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, but the description adds provenance semantics for id (it must come from search_opportunities within this MCP server, and invalid ids cost nothing because they 404 before payment). The days parameter is left entirely to the schema, which documents it adequately.

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 resource and shape: daily history of one opportunity's APY, TVL and risk scores, keyed by a single id. It distinguishes itself from siblings like get_opportunity_score and get_opportunity_card by being a time series rather than a point-in-time view, and it names the sibling that produces the id.

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?

'Useful for checking whether a yield is stable or newly inflated, and for trend charts' gives concrete usage contexts, and it explicitly routes the agent to search_opportunities for the id. It stops short of saying when NOT to use it (e.g., for a single current snapshot, use get_opportunity_score instead).

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