Current limits

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

With no annotations provided, the description carries the full burden and handles it well. It discloses the security-sensitive behavior (reads credentials from macOS keychain, sends them only to api.anthropic.com), the side effect of record=true appending to a log file, and the data volatility of the breakdown (gone after the weekly window rolls over). This is rich, useful behavioral context.

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 description is longer than average but every clause earns its place: purpose first, then security, then the record side effect and its rationale. It is front-loaded with the primary function and well-structured, though slightly dense with the parenthetical breakdown details.

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 tool with a single optional parameter and no output schema, the description covers the essentials: what is queried, security behavior, side effects, and data lifecycle. The only gap is that it does not describe the shape of the return value, but given no output schema exists and the tool is simple, this is a minor omission.

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% for the single record parameter, so the baseline is 3. The description goes beyond the schema by explaining what record=true accomplishes (appends one sample to data/usage-log.jsonl) and why it is worth setting — the breakdown is lost after the window rolls over. This adds genuine value beyond the schema definition.

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 action and resource: 'Asks Anthropic what is left right now' — covering 5-hour, weekly, and per-model (Fable) limits plus a per-product breakdown (Claude Code / chat / Cowork). This is specific and clear about scope. It doesn't explicitly name siblings like limit_breakdown to differentiate itself, but the per-product breakdown detail implies a distinct scope.

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?

There is no explicit when-to-use guidance or reference to alternatives. The only usage hint is 'worth recording now and then', which implies periodic use but does not explain when to choose this tool over subscription_value, limit_breakdown, or chat_share. No exclusions or alternative routing is given.

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