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

With no annotations, the description carries the full burden. It explicitly states that the tool is 'deterministic and fixture-verified', that guest invocation is 'free within rate limits', and that 'every completion returns a signed provenance envelope'. This provides strong confidence about safety, cost, and response shape, though it does not literally say 'read-only' or 'no side effects'.

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 three sentences, front-loaded with the primary purpose. Every clause adds information: the list scope, the returned fields, determinism, cost, provenance, and a pointer to identity documents. No filler or repetition exists.

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 metadata-list tool with an output schema present, the description is complete. It covers what is listed, the behavioral guarantees, the cost model, and the response envelope. Nothing important is missing for selecting and invoking this tool.

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 has zero parameters and the schema is 100% covered, so there is no parameter detail to add. The description compensates by summarizing the output fields and the signed provenance envelope, helping an agent understand what a no-input invocation will yield. This exceeds the baseline for a no-parameter tool.

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?

Description opens with a specific verb ('List') and resource ('Agent Guild's invocable utility capabilities (the ag_* tools)'), then enumerates the exact return contents (id, version, summary, input/output JSON schemas, latency, guest terms). This clearly distinguishes it from the sibling guild_* tools, which target different facets of the Agent Guild.

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 usage is implied: this is the tool for discovering ag_* capabilities, and it even points to an alternative source for identity documents (GET /.well-known/ag-identities/index.json). However, it does not explicitly state when to use this tool instead of sibling tools like guild_index, nor does it provide when-not-to-use guidance or contrast with alternatives.

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