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

readOnlyHint=true already marks this as a safe read, so the burden is light. The description does add value by naming the response contents (status, output, error), which is useful given there is no output schema, but it says nothing about behavior on a missing run, error cases, or auth.

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?

Two short, front-loaded sentences with no filler; the returned fields are stated before the API reference. The trailing "Inngest: GET /v1/runs/{runId}" line is a useful anchor rather than padding.

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 single-parameter read tool whose schema is fully documented and which has no output schema, the description covers purpose, the identifier, and the returned fields. Only edge-case behavior (missing run, auth) is absent, which is a minor gap.

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%, so the sole run_id parameter is already documented as a ULID. The description adds only the endpoint path template, which is marginal; the baseline of 3 applies when the schema carries the parameter meaning.

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?

States a specific verb and resource ("Fetch a single function run") and enumerates what it returns (status, output, error), which cleanly separates it from list-style siblings like list_run_jobs and list_event_runs. It stops short of explicitly naming a sibling it is not, so it is clear but not maximally differentiated.

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 says what it does but never says when to use it versus siblings, nor how to obtain a run_id (e.g., via list_event_runs). No prerequisites, no exclusions, no alternative routing is supplied.

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