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

Annotations already convey read-only, idempotent, non-destructive behavior. The description adds useful behavioral context by specifying that results are per election cycle and that a cycle filter narrows the response. It does not disclose default ordering or handling of absent cycles, but with annotations covering safety, this is strong enough.

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 tight, front-loaded sentences. The core action and resource appear first, and the field list plus filter instruction are packed without redundancy.

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 read-only lookup with no output schema, the description names the main return fields and the filtering dimension. It leaves default pagination/limit behavior to the schema, which is acceptable given the annotations. A fully explicit note about multi-cycle default behavior would push it to 5.

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 has 100% coverage for all three parameters, so the baseline is 3. The description adds value by linking cycle to the election-cycle breakdown and clarifying its role as a filter, going slightly beyond the schema text.

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 names a specific verb ('Get'), a specific resource ('aggregate campaign finance totals for a candidate by FEC candidate_id'), and the breakdown dimension ('election cycle'). It also lists the included fields, which clearly differentiates it from sibling tools like fec_candidate_details and fec_candidate_search.

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 clearly states when to use it: for campaign finance totals of a candidate, and gives a concrete filtering instruction ('Filter to one cycle with the cycle parameter'). It does not explicitly name alternatives or exclusions, so it misses the top score.

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