session_stats

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false. The description adds the output characteristic 'aggregate numbers, not per-session rows,' contrasting with session_list. It also clarifies the target parameter source, but does not disclose any other behavioral traits (e.g., error handling or data freshness). This is adequate given the strong annotation coverage.

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 extremely concise and well-structured. It opens with a clear [READ] tag and a one-line summary, then adds the key distinction from session_list, and finishes with a compact Args section. Every sentence contributes value with no redundancy.

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?

Given the simple schema (1 optional param), strong annotations, and no output schema, the description provides sufficient context: it summarizes the output dimensions (state/protocol concurrency, current concurrent, busiest pools) and clarifies it is aggregate data. It could be slightly more detailed about how the output is presented, but overall it is complete for an agent to select and invoke correctly.

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?

With 0% schema description coverage, the description compensates by explaining the single parameter: 'target: Horizon target from config.yaml; omit to use the default.' This adds meaning beyond the bare schema (which only lists a name and default), though it could be slightly more explicit about what 'target' represents in the context of session statistics.

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 clearly states the tool's function: 'Session statistics: concurrency by state / protocol, current concurrent, busiest pools.' It uses a specific resource (session statistics) and identifies the scope, distinguishing it from session_list by explicitly noting it provides 'aggregate numbers, not per-session rows.'

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?

It gives clear usage context by saying it is 'The reporting counterpart to session_list — aggregate numbers, not per-session rows,' which directly tells the agent when to prefer this over the sibling session_list. However, it does not mention other alternatives or exclusions, so it falls short of a 5.

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