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

Annotations already establish this as a safe read (readOnlyHint=true, destructiveHint=false), so the description only needed to add scope, and it does: it enumerates the returned fields and explicitly warns that patch bodies are absent, preventing an agent from assuming diffs come back. It does not cover auth, rate limits, or behavior for unknown SHAs, which keeps it below a 5.

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?

Three tight clauses with zero filler: what it returns, how it maps to the underlying endpoint, and the one thing it deliberately omits. The critical exclusion is front-loaded right after the scope statement.

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 read-only single-resource fetch with no output schema, the description supplies the closest thing available: an explicit field list of what comes back and a clear statement of what does not. Nothing an agent needs in order to call it correctly is missing.

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?

With only 50% schema coverage, the description carries real weight: it explains that lookup is keyed by SHA and that the default payload includes the files-changed list, which is the meaning behind the include_files flag. The REST path it cites also grounds owner/repo, though those two parameters are still not described anywhere.

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 pairs a specific verb and resource ('Fetch a single commit by SHA') with the exact payload contents (metadata, changed files with path/status/additions/deletions) and maps itself to GET /api/v2/repos/.../commits/:sha. That is enough for an agent to distinguish it from siblings like merjax_get_diff or merjax_list_tree without opening any 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?

It gives an explicit exclusion plus the alternative: 'Patch bodies are NOT included — use merjax_get_diff for those,' which is the main routing decision an agent faces here. What is missing is guidance on when to prefer this over other commit-level lookups (e.g. workflow runs or PR views), but the primary fork is covered.

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