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

readOnlyHint=true already establishes this is a safe read, so the description isn't carrying the safety burden. It adds the REST endpoint mapping and the either/or parameter constraint, which is useful context. It doesn't disclose return shape, pagination, or error behavior, so a 3 is appropriate.

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 sentences, front-loaded with the action, then the invocation rule, then the REST mapping. Nothing is wasted and the most decision-relevant information comes first.

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 list tool with a fully documented 6-parameter schema and annotations covering safety, the description is nearly complete: purpose, input rule, and endpoint. The only omission is any hint about the shape or volume of what is returned, and there is no output schema to cover that.

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 coverage is 100%, so the schema documents each parameter and the baseline is 3. The description goes beyond the schema by stating the mutual-exclusion rule between base/head and pullid, which the individual field descriptions only imply. That is genuine added 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?

The description gives a specific verb and resource: 'List the files whose coverage changed between two commits or for a pull request.' That is clearly distinguishable from most siblings. However, it never differentiates itself from codecov_compare, its nearest sibling, so it stops short of a 5.

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 explicit operating constraints for the inputs: 'Provide EITHER both `base` and `head`, OR `pullid`.' That tells the agent how to invoke it correctly. It doesn't say when to prefer this over codecov_compare or the other coverage tools, so no 5.

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