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

Annotations already cover safety (readOnly, idempotent, non-destructive, openWorld), so the bar is lower, and the description adds genuinely new behavioral context: slots and measurements are never summed or swapped, and an unfetchable board yields a distinct UNREACHABLE state with no cached number ever shown as live. That failure-mode disclosure is the kind of detail annotations cannot express.

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 first sentence front-loads purpose and source well, but the body is a long chain of em-dash-appended clauses that mixes return-value definition, parameter selection, and a mission statement ('We measure, never certify'), which borders on redundant given the output schema exists. It is readable but heavier than the single-parameter, output-schema-backed tool needs.

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 an output schema present, return values need not be spelled out, yet the description covers the semantic pitfalls (slot vs. measurement, never summed) and the error state, which are the pieces structured fields cannot carry. Only the routing among sibling evidence tools is left unexplained.

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 description coverage is 100% and the single enum parameter is fully documented in the schema, so baseline 3 applies. The description's detail="full" clause largely restates the schema ('count_grammar, per-family counts, measured_on block') rather than adding format or cost semantics.

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 resource (live GSPC board totals) with a concrete verb-equivalent (fetch/return) and enumerates exactly what comes back: slot count, measured count, separation line, and as_of dates. It does not, however, differentiate itself from the many sibling evidence/trust tools (measurement_index, get_axis, get_card), leaving the agent to infer the distinction.

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?

Usage is only implied: the tool is the way to read board totals, and the description tells the agent to pass detail="full" for the long-form grammar and per-family counts, which is a useful selection cue. But there is no explicit when-to-use vs. siblings or when-not to use it, so guidance stays at the implied level.

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