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

Annotations carry the read-only safety profile, and the description adds genuinely beyond it: truncation at max_bytes with an explicit truncation note, and a named failure mode (unsupported_content) for binary input. It stops short of auth requirements or how truncation interacts with large files, but the disclosed behavior is well above the annotation baseline.

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 tightly packed sentences with no filler; the primary action and its constraint come first, with the failure mode and escape hatch immediately after. Every clause carries information.

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?

With no output schema, the description still tells the agent what it gets back (text content, possibly truncated with a note) and what errors to expect. Missing only edge details such as behavior on nonexistent paths or very large max_bytes, which are minor for a simple read 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?

Schema description coverage is 100%, so path, run_id, and max_bytes are already documented with types and the 65536 default. The description merely restates the max_bytes default and the text-only constraint rather than adding format or syntax guidance, so the baseline 3 applies.

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?

Specific verb+resource ("Fetch one artifact file's TEXT content") with a clearly bounded scope: a single file, text only. The words "one" and "TEXT" implicitly separate it from the sibling mcg_fetch_artifacts (plural) and from binary retrieval, so an agent can route correctly without opening a schema.

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?

Gives a clear when-not rule (binary content REJECTS) and points to an alternative destination ("the run's public page") for binaries. It does not explicitly contrast with the sibling mcg_fetch_artifacts for multi-file retrieval, so usage is clear but not fully exhaustive.

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