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

With only readOnlyHint available, the description carries the behavioral burden richly: silent truncation to the first 6 unique tickers, missing-XBRL tickers returned as {available:false} rather than dropped, one cold EDGAR fetch per ticker (latency hint), and the data source. This is well beyond what annotations provide.

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 purpose, then constraints and return shape. Dense but every sentence earns its place -- truncation behavior, return keys, unit conventions, fiscal-year caveat, and edge case are all load-bearing.

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?

No output schema exists, but the description fully specifies the return envelope {summary, count, peers, as_of} and per-peer keys, plus unit conventions (whole USD, *_pct as numbers) and the non-aligned fiscal-year caveat. Nothing an agent needs to call and interpret it is missing.

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% and documents the 2-6 array, but the description adds critical semantics the schema omits: extras are dropped silently and it's the FIRST 6 unique tickers that are kept. That clarifies de-duplication and truncation order, which the schema alone does not convey.

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 ('side-by-side latest-fiscal-year fundamentals for a peer set') and immediately differentiates from the sibling get_fundamentals by declaring 'ONE YEAR ONLY -- no history (use get_fundamentals).' An agent can identify this tool's scope 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?

Names the alternative for historical data explicitly and clarifies what the tool cannot do ('no price leg, so no P/E or EV multiples'). It provides clear context for when to reach for it, though it doesn't spell out a full when-not-to-use matrix beyond the history case.

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