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

Annotations already declare readOnlyHint=true, openWorldHint=false and destructiveHint=false, so safety is covered. The description does add useful behavioral context: the result space is empirically grounded in the 'Modkeel lab' and returns one of three states including 'never tested together,' which warns the agent that a null-ish answer is possible. It says nothing about caching, freshness, or version scoping beyond the schema.

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 tight sentences with the substance front-loaded; nothing is padded. The trailing fragment 'By mod id.' is clipped rather than wasteful, and it does convey the lookup key.

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?

An output schema exists, so return values need not be explained, and the three statuses named in the description map onto the likely result shape. With full schema coverage and annotations covering the safety profile, the only real gap is the absence of guidance about the optional mc version parameter and sibling routing.

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% (mod_a, mod_b, mc all documented with examples), so the schema carries parameter meaning. The description's 'By mod id' only confirms the lookup keys and adds nothing about the optional mc parameter's effect on results. 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?

The description names the exact resource (a pair of Minecraft mods) and the exact question answered (ran together, clashed, or never tested), which is far more specific than the bare name 'mod_pair'. It does not, however, contrast itself with siblings diagnose_crash or mod_lab_runs, so the agent must infer the boundary.

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?

There is no statement of when to reach for this tool versus diagnose_crash or mod_lab_runs, and no prerequisites (e.g. whether both mod ids must already exist in the lab). Usage is only implied by the phrase 'By mod id.'

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