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

Annotations already cover readOnly/idempotent/non-destructive, so the bar is lower, and the description still adds a domain-specific trait: 'Does not consume a checkpoint write,' which tells the agent this probe is free of quota side effects. It also implies reading live rather than cached state ('actual plan'). It does not say what the response contains or whether results are cached.

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?

Three short, front-loaded sentences with no filler; the core purpose leads and the operational caveats follow.

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 zero-parameter, read-only probe with no output schema, the description covers what is read, its side-effect-free nature, and the key workflow. Minor gap: it never hints at what fields come back (plan name, remaining count), which an agent building on the result would want.

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 tool takes no parameters (additionalProperties: false), so the baseline of 4 applies; there is nothing for the description to disambiguate.

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 actual plan and checkpoint usage'), which is more precise than the title's vague 'Check plan and remaining capacity'. It does not, however, explicitly differentiate itself from the sibling threadkeep_plans, which an agent could easily confuse for a plan-status lookup.

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 concrete triggering workflow: 'Verify plan=pro after the user pays before resuming a blocked save.' That is a real when-to-use condition tied to sibling tools (resume, checkpoint). It stops short of naming alternatives or stating when not to call it (e.g. versus threadkeep_plans).

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