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

Annotations already declare readOnly, idempotent, and non-destructive, so safety is covered. The description adds genuine behavioral context the annotations do not: the per-file line-diff format, the sign convention, and that each header names its version — important since there is no output 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?

Three tight sentences, front-loaded with the core comparison semantics, then the argument convention, then the id source. No filler and 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 usefully describes the return shape (line diff per file, headers naming versions). Combined with annotations and the schema-documented projectId, an agent has what it needs; only an explicit alternative-tool contrast 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?

Schema coverage is only 33% (sourceBranch and targetBranch are bare), so the description must carry weight and does: the '-'/'+' sign convention plus 'pass the version it was made from as sourceBranch' defines exactly what each branch argument means. projectId is already documented in the schema.

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+resource ('Show what changes from sourceBranch to targetBranch') and immediately pins down the output convention. It is clearly distinguishable from merge_branch, switch_branch, and list_branches, which are the nearest siblings.

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 concrete usage condition ('To see what a version changed, pass the version it was made from as sourceBranch') and routes the agent to list_branches for ids. It lacks an explicit when-not-to-use contrast with merge_branch/switch_branch, but the directionality guidance is strong.

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