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

With no annotations provided, the description carries the full burden. It explicitly states 'Read-only; no side effects, auth, or rate limits' and adds performance behavior for include_token_total ('measurably slower on large vaults'). It also discloses the conditional by_project breakdown, providing rich behavioral context beyond any schema.

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 sentences deliver high information density: purpose, parameters, side effects, performance caveat, and an alternative tool. Every clause earns its place, and the use of backticks for parameters improves scannability.

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 three optional parameters, no output schema, and no annotations, this description is remarkably complete. It covers purpose, usage, behavior, parameter nuances, side effects, auth, rate limits, performance, and alternatives, leaving little ambiguity for an agent.

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 schema already documents all three parameters (100% coverage), so the baseline is 3. The description adds value beyond the schema by explaining the performance impact of include_token_total and clarifying that omitting project_id yields an additional by_project breakdown. However, top_tags receives no extra semantic context beyond the schema description.

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 starts with a specific verb and resource ('Aggregate counts for a scope') and lists concrete aggregates (file_count, untagged_count, favorite_count, top_tags). It also differentiates from sibling tools like diff_against_disk by referencing 'cheap dashboard' vs 'live disk-vs-index drift'.

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 tells when to use the tool ('Use as a cheap dashboard or to spot untagged content for cleanup') and when not to, naming an alternative: 'for live disk-vs-index drift use diff_against_disk'. It also explains the distinction between omitting project_id vs passing null.

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