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

Beyond the annotations' read-only/idempotent/destructive hints, the description discloses that the data is cached for up to an hour, requires an Authorization Bearer token (and returns setup steps without it), returns rows in descending 90-day alpha order, and only covers disclosed purchases with a full 90-day window. It also explicitly warns it is not a forecast. This is substantial added behavioral context.

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 description is a single dense paragraph, but it front-loads the core purpose and flows through eligibility, usage, output order, method, disclaimers, auth, and caching. Every sentence adds operational detail; however, the breadth of topics makes it less scannable than a bulleted structure, though it remains efficient.

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 lists every field that will appear in each row (number of purchases, average 90-day return, S&P average, 90-day and 30-day alpha, hit rate, member page) and states the response will describe the method. It also covers eligibility, exclusions, auth failure mode, and cache lifetime. Given the tool's two simple optional parameters, the description is fully adequate for correct invocation.

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?

Since the input schema already documents both limit and min_trades with 100% coverage, the baseline is 3. The description adds one meaningful constraint: members must have min_trades priced purchases that have a full 90-day window, which clarifies the window requirement not present in the schema. It does not add new information about limit, but the min_trades clarification warrants a 4.

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 opens with the exact computation—per-member 90-day return on disclosed stock purchases versus the S&P 500, including 30-day alpha and hit rate—so the agent knows the resource and metric. It further distinguishes this tool from congress_leaderboard by stating that the latter ranks activity and carries no returns. This makes the purpose unambiguous and separated from siblings.

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?

The tool explicitly states 'Use it when the question is about performance' and contrasts congress_leaderboard as the activity-ranking tool without returns. This gives the agent both a positive trigger and an explicit alternative, covering the when/when-not distinction. It does not reference the other eight siblings, but the performance/activity split is the key decision point.

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