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

With only readOnlyHint=true in annotations, the description carries the burden and adds substantial behavioral context: the return shape, the denominator caveat ('REPORTED 13F long-equity value, explicitly NOT AUM'), refusal on unreachable store ('DATA_UNAVAILABLE'), no fabricated turnover for single-quarter filers, and source/licensing details. These are 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?

The description is dense but front-loaded: purpose first, then input constraint, return keys, denominator caveat, sibling disambiguation, edge cases, and source. Every sentence carries actionable information for correct invocation or interpretation, with no filler.

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?

Given no output schema, the description adequately explains the return object keys and the denominator semantics. It also covers refusal behavior, single-quarter limitations, and where caveats appear ('tool_notes'), making it complete for an agent to call and interpret the tool.

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 schema already documents the single 'fund' parameter. The description adds meaning by requiring a numeric CIK and warning that a ticker will not resolve, plus pointing to ol_13f_filer_search for lookup. This is useful clarification beyond the schema example, though it does not elaborate on format beyond 'numeric CIK'.

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 states a specific verb+resource and scope: 'Institutional-filer behavior derived purely from 13F holdings: concentration (top-N %, normalized HHI), turnover, and persistence... for one filer.' It explicitly distinguishes from siblings by noting 'ol_13f_filer_search finds it' for CIK lookup and 'NO position list -- use get_13f_holdings' for holdings, so an agent can route correctly without opening other schemas.

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 gives explicit usage constraints: 'Pass a NUMERIC CIK (a ticker will not resolve here; ol_13f_filer_search finds it)' and names the alternative for position-level data: 'NO position list -- use get_13f_holdings.' It also states edge-case behavior for single-quarter filers and unreachable stores, leaving little to inference.

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