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

With no annotations provided, the description carries the full burden of behavioral disclosure. The phrase 'value discarded' and the parameter annotations like 'discarded after the shape check' reveal that the tool has side effects of discarding input values)Skip that but it doesn't explain what the tool returns (e.g., a boolean, error message) or what happens on invalid input. It also doesn't warn about potential rate limits or required authentication, leaving the agent uncertain about the call's 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?

The description is extremely concise (5 words) and front-loaded with the key purpose. It avoids fluff and every word earns its place. However, the extreme brevity lacks necessary context for a tool with 9 parameters, so it feels more like under-specification than refined conciseness.

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?

Given the complexity - 9 diverse parameters covering refs, URLs, city names, JSON, paths, timezones, and search queries - a one-line description is insufficient. The presence of many sibling tools (e.g., 'normalize-url', 'validate-json', 'weather-hint') suggests this tool may unify format checks, but the description doesn't clarify how the parameters relate to XID or what the output is. The schema and output schema do not compensate, so an agent would struggle to call it correctly.

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?

Schema description coverage is 100%, meaning each parameter's description is present in the schema, but the description text adds little beyond that. The tool description does not explain how parameters like 'ref', 'url', or 'query' relate to the XID shape check; it only repeats that they are discarded. The schema descriptions are concise but the overall purpose of having 9 heterogeneous parameters is unclear, so the description adds marginal value.

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 'XID charset and length, value discarded' clearly states a specific purpose (validating XID shape) and indicates that the value is not retained. However, it does not explicitly differentiate it from siblings like 'domain-shape' or 'file-path-ok', which likely have analogous shape-checking roles, though the resource (XID) is specific.

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 implies that the tool is for validating the shape (charset and length) of an XID, which gives some usage context. However, it provides no explicit guidance on when to use this tool over alternatives like 'github-repo-shape' or 'jira-key-shape', and it does not mention any exclusions or preconditions.

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