Summarise the local usage log

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

Annotations already declare readOnlyHint=true and openWorldHint=false; the description adds real context beyond them by naming the data source, saying it 'reads local files only and runs no Codex process', and bounding what the result can contain. It stops short of stating behaviour when the log is absent or empty, or how much data a large window returns.

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 sentences, front-loaded with the core action and payload, with the scope caveats following immediately. Every clause (source file, windowing, reported fields, local-only, no quota) carries distinct 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?

With only two fully-documented optional parameters and no output schema, the description does the right extra work by listing the reported fields, which stands in for a return-value spec. The remaining gap is edge-case behaviour (empty or missing log, size of output for long windows) for a tool the agent will likely call with defaults.

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 both parameters (including the enum and its default) are already fully documented in the schema. The description's 'over a window' and 'per group' merely gesture at the same two parameters without adding syntax, bounds or examples, so baseline 3 applies.

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 ('Summarise this server's local usage log (CODEX_SUBAGENT_USAGE_LOG)') and enumerates exactly what the summary contains: process counts, outcomes, commands, durations and reported tokens. That combination is unmistakable against every sibling, none of which summarise usage history.

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?

Gives a clear usage context (summarising the local log over a window) and an explicit exclusion ('It never reports quota, credits or remaining allowance'), which steers an agent away from asking it about allowance. It does not name an alternative tool for quota-style questions, so it falls short of full when/when-not routing.

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