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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description adds a non-obvious behavioral detail: unknown IDs return found:false rather than an error or empty result. This is useful operational context beyond what annotations and the schema 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?

Two short sentences front-load the action and parameter, with no filler. The second sentence adds a high-value behavioral fact without bloating the description.

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 one-parameter read-only lookup with an output schema, the description covers the essential behavior: exact lookup by instrument ID and the not-found outcome. Nothing critical is missing for an agent to select and invoke the tool correctly; the output schema covers return structure.

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?

The input schema provides no description for the sole id parameter (0% coverage), so the description must fill that gap. 'by instrument_id' tells the agent that id is the instrument's unique identifier, and 'unknown ids return found:false' further clarifies its role; for a single simple parameter this is sufficient semantic compensation.

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 a specific verb and resource: 'Lookup one instrument by instrument_id,' which clearly identifies the tool's function and distinguishes it from the list and search siblings by specifying a single exact-key lookup. The added 'Unknown ids return found:false' reinforces that this is an exact ID query, not a fuzzy 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?

The phrase 'by instrument_id' clearly establishes the usage context: use this tool when you have an exact instrument identifier and need one matching record. It does not explicitly name alternatives or when-not-to-use, so it stops short of a 5, but the lookup-by-id framing gives an agent clear guidance relative to search/list siblings.

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