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

Annotations only cover safety/idempotency; the description adds the behavior that matters here: it consumes no score, returns no verdict, is never billed, and that an unrecognized or non-sg_live_ key returns invalid_api_key with no fallback. It also discloses tier caps (1,000 vs 100 per UTC day) and the next-midnight reset semantics.

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?

Purpose and sibling comparison are front-loaded, then parameter rules, then return fields. The returns enumeration is long, but with no output schema it earns its place; the prose is dense rather than padded.

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 single-optional-parameter read with no output schema, the description covers tuning inputs, failure modes, rate-limit tiers, and the full return shape. Nothing an agent needs to invoke or interpret this correctly is missing.

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 baseline is 3, but the description goes further by tying api_key to the sg_live_ prefix, contrasting it with the anonymous bucket when omitted, and specifying the invalid_api_key failure mode. It adds real routing meaning beyond the schema's field description.

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 and resource ('Read today's free-score balance') and immediately distinguishes itself from the sibling score_spend and from get_api_key (used to mint a higher cap). An agent can identify this as the non-billing, non-verdict quota read without opening any schema.

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?

Explicit routing: prefer this over score_spend when not judging a specific payment, including before a batch or after a 402, plus a clear exclusion ('Do not use it to approve or block a spend'). Both the when and the when-not are stated with the alternative named.

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