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

Annotations already mark readOnlyHint=true and destructiveHint=false, and the description adds valuable behavior beyond that: server-side pair ordering normalization and the array-shaped response pattern. It does not mention pagination or auth, but these are less critical for a read-only lookup.

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, information-dense sentences. The core operation and access modes are front-loaded, and no sentence repeats schema or annotation information.

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?

Covers lookup modes, tuple semantics, optional mapping_method, pair-order normalization, and return shape. The only notable gap is that the schema marks all parameters optional while the description implies at least an id or tuple should be supplied, but does not explicitly state that constraint.

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?

Despite 0% schema description coverage, the description compensates by explaining how id, construct_id, instrument_a, instrument_b, and mapping_method combine into meaningful lookup modes. It also clarifies that instrument_a/b order is irrelevant. The id parameter gets less explanation, but 'by id' is self-explanatory.

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 ('Look up') and a specific resource ('InstrumentEquivalence rows'), and enumerates the exact access paths: by id or by canonical tuple. This distinguishes it from sibling search tools, which imply broader or fuzzier result sets.

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 description clearly indicates when to use this tool: when you have an id or the construct/pair/method tuple. It also notes the optional mapping_method. It does not explicitly state 'use search when you lack exact identifiers', but the lookup-vs-search distinction is strongly implied.

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