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

readOnlyHint=true is consistent with a static reference list, and the description adds genuine context: it is the canonical source of 'the label every answer uses' and clarifies these are derivatives on the venue, not equity shares. It does not say whether the list changes over time, whether it requires authentication, or how it relates to the live-state sibling — modest but real added value over the annotation.

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 resource and kept to two sentences plus a short clarifying fragment — appropriately sized for a parameterless catalog tool. The phrase 'the label every answer uses' is slightly cryptic and the final sentence is telegraphic, but neither adds bloat.

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 parameters and an output schema present, the description needn't explain return values, and it does convey the domain (SpaceX/Circle perpetuals on Aster, BNB Chain). What is missing is the relationship to instrument_spec and instrument_state — the single question an agent will actually have when four instrument-prefixed siblings are listed.

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 tool takes zero parameters, so there is nothing for the description to disambiguate; baseline 4 applies. The prose field list (venue, contract, chain, fees, funding cycle, session policy) loosely maps to what the response carries, though the output schema already covers that.

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 resource (the instrument list for the ChainHelix instrument lane) and enumerates the fields returned: venue, contract, chain, fees, funding cycle, session policy. It does not, however, distinguish itself from near-identical siblings such as instrument_spec, instrument_state, or instrument_signals, so an agent must guess which of the four to call.

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?

No when-to-use guidance and no named alternatives despite four closely related sibling tools (instrument_spec, instrument_state, instrument_signals, verify_instrument_signal). The description never says whether this is the reference catalog to consult first, or how it relates to the live-state or per-instrument lookups.

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