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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false. The description goes well beyond by disclosing the exact return envelope ({ meta, job }), the flat Job shape matching search_jobs, the critical id-format caveat (NOT prefixed with source name), the composite ATS format with a concrete example, and the error behavior for unsupported sources. This is rich behavioral context that adds real value.

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 core function, then progressively adds essential caveats. Every sentence contributes unique information (return shape, id rules, source limitations) with no filler or redundancy.

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 2-parameter, simple fetch tool with no output schema, the description covers everything an agent needs: the return shape, id semantics, ATS exception, and error behavior when a source doesn't support single-job lookup. The sibling search_jobs is referenced, and the safety profile is already in annotations. No significant gaps exist.

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 input schema already provides 100% coverage with descriptions for both parameters, so the baseline is 3. The description adds valuable semantics beyond the schema: it emphasizes that the id is the native upstream id as returned by search results, explicitly warns against prefixing with source name, and details the ATS composite format for round-tripping. This extra context justifies a 4.

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 opens with a specific verb+resource+scope: "Fetch one job posting by its source engine and native id, returned as { meta, job } with the same flat Job shape search_jobs yields." This clearly distinguishes it from the sibling search_jobs (single vs. list) and fully conveys the tool's purpose.

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 provides clear usage context: it specifies the input (source + native id), explains the id semantics, and notes when the tool cannot be used ("Not every source supports single-job lookup — a search-only source returns a not_supported / not_found error"). However, it does not explicitly say "use search_jobs instead when you need to list jobs," so the alternative guidance is implicit rather than explicit.

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