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

The description adds value beyond annotations by specifying the exact fields returned and explicitly stating that provider credentials and configuration are never returned. This complements the readOnlyHint, idempotentHint, and destructiveHint annotations by detailing the data exposure.

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 description is concise with three sentences, each providing distinct information: what the tool does, what it does not return, and permission/API reference. It is front-loaded with the core functionality.

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?

Given the presence of an output schema, the description satisfactorily covers the tool's purpose, limitations, and permission. It omits potential error cases or prerequisites, but for a simple get operation, this is acceptable.

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 100% schema description coverage, the description adds minimal additional meaning beyond the schema. The phrase 'by stable identifier' is already implied in the parameter description. The baseline score of 3 is appropriate.

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 clearly states it returns one enabled sender identity by stable identifier, listing the specific fields returned (name, address, provider type) and explicitly noting what is not returned (credentials and configuration). This distinguishes it from the sibling tool 'sender_identities_list', which presumably returns multiple identities.

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 description implies usage when a specific sender identity is needed by identifier, but it does not explicitly state when not to use it or mention alternatives like 'sender_identities_list'. It provides clear context for its single-item retrieval purpose.

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