capabilities_index

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

The description discloses that the tool writes/regenerates the index, and importantly explains the read-only CI behavior ('fails instead of writing on drift'). This complements the readOnlyHint: false annotation by giving concrete failure semantics, though it does not detail side effects or required permissions.

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 action and resource, then usage timing, then the parameter mode. Every sentence earns its place with no filler or repetition.

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 simple one-parameter write tool with no output schema, the description fully covers what the tool does, when to use it, and how the parameter changes behavior. The inclusion of failure mode in CI makes it operationally complete.

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?

The input schema already fully describes the 'check' parameter with high coverage, and the description adds practical context by explaining the CI-mode behavior. This reinforces the schema without redundancy, raising it above the baseline.

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 opens with a specific verb ('Regenerate') and a clear resource ('CAPABILITIES.yaml'), identifying it as the package's coverage index. This distinguishes it from sibling tools like list_skills or list_rules, which query rather than update the index.

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?

The description explicitly says 'Use after adding or removing an artifact to keep the index current,' which is clear guidance for when to invoke it. It also explains the CI-mode use case with 'check: true', but does not name alternative tools to use instead of this one, such as list_* commands.

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