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

Annotations already cover the safety profile (readOnlyHint=true, idempotentHint=true, destructiveHint=false), so the bar is lower. The description adds value beyond that by disclosing the response scope ('full detail... includes office, party, status, election years, and mailing address'), giving the agent a concrete expectation of what comes back. It doesn't mention behavior for invalid IDs, but that's a minor gap for a simple lookup.

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?

Two sentences, no filler. The first establishes purpose with an example; the second routes to the sibling tool. Both sentences earn their place and the core action is front-loaded.

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 single-parameter, read-only lookup, everything needed to invoke it correctly is present: the parameter is fully documented, the return content is described (field list compensates for the absent output schema), annotations cover safety, and the prerequisite relationship to fec_candidate_search is stated.

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% — the schema already documents candidate_id with two examples ('P80001571', 'S2MA00170'). The description repeats one example but adds no meaning beyond what the schema provides, 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?

The description uses a specific verb-resource pair ('Get full detail for a single federal candidate') and identifies the lookup key (candidate_id) with a concrete example. It also enumerates the included fields (office, party, status, election years, mailing address), which distinguishes this from the financial-oriented sibling fec_candidate_financials.

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?

It explicitly routes to fec_candidate_search when the ID is unknown ('Use fec_candidate_search to find the candidate_id'), which is clear when-not-to-use guidance. However, it doesn't explicitly address the other FEC siblings (fec_candidate_financials, fec_committee_search); the field list implies the boundary, but an explicit exclusion would make it fully complete.

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