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

Annotations already cover read/write safety (readOnlyHint=false, destructiveHint=false, idempotentHint=true). The description adds one useful behavioral detail: 'Returns 404 if the source slug is not found.' However, it does not disclose what happens to any previously assigned source or other side effects beyond 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?

The core action and error behavior are expressed in two concise sentences. The only mild redundancy is the opening 'Update Review Source' line repeating the tool title, but the rest is front-loaded and free of filler.

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 two-parameter tool with an output schema and safety annotations, the description covers the essential action, the requirement that the source already exists, and the 404 failure mode. It is sufficiently complete for an agent to know how to invoke the operation correctly, though it could note whether an existing assignment is replaced.

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 the parameter descriptions already document id and source_slug. The description's mention of 'existing review source' and '404' largely repeats the schema's own text for source_slug, adding no new parameter-level meaning beyond what the input schema provides.

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 states a specific operation: 'Assign an existing review source to a review by slug.' This clearly identifies the verb (assign), resource (review source), and target (review), and distinguishes it from sibling tools like updateSource (which modifies source settings) or createSource (which creates sources).

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?

The usage context is implied: use when you need to attach an existing review source to a review. However, it does not explicitly name alternatives or state when not to use this tool, unlike sibling tools such as updateSource or createSource, leaving the agent to infer the boundary.

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