Corpus coverage status

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

With readOnlyHint=true already covering the safety profile, the description adds real behavioral context: it discloses what is excluded by default (research_private/restricted) and that the call takes no arguments. It does not mention cost, refresh latency, or whether the counts are cached, but the exclusion disclosure is the important non-obvious behavior.

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?

Front-loaded with the returned content, then the diagnostic use case, then the no-argument note. Dense but every clause carries information, though the enumerated field list is a slightly long prepositional run-on.

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?

There is no output schema, so the description carries the return-shape burden and does so by enumerating the reported categories. Combined with the exclusion note and no-argument statement, an agent has everything needed to decide whether to call it and how to read the result.

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?

Zero-parameter tool, so the schema baseline is 4. The description explicitly confirms 'Takes no arguments,' removing any doubt that filters could be applied, though it adds nothing further since there are no parameters to explain.

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 names a specific resource (the local nabu corpus) and enumerates exactly what status it reports: per-source document/passage counts, last-sync recency, language and license-class breakdowns, index state, and default exclusions. That scope is clearly distinct from the sibling query tools (nabu_search, nabu_concord, nabu_show), which retrieve texts rather than describe coverage.

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 an explicit trigger: call this to interpret an empty search before concluding a text is unattested, and frames the diagnostic questions (language, source, period ingested?). It stops short of naming a specific alternative tool or stating when-not to call it, which keeps it from a 5.

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