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

The description goes beyond the readOnly/idempotent annotations by disclosing the exact returned fields, the two credential types supported, and the null behavior for OAuth-specific fields under instance keys. This is meaningful behavioral context an agent cannot infer from the schema or annotations alone.

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 with no filler: the first front-loads purpose and output fields, the second adds compatibility detail, and the third clarifies null behavior. Every sentence contributes useful 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?

The combination of annotations (read-only, idempotent, non-destructive), empty input schema, and a description that covers output fields, credential types, and null cases makes this fully adequate for an agent to invoke correctly without further context.

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?

This is a zero-parameter tool with an empty schema and 100% schema coverage, so there is no parameter burden for the description to carry. The description adds value by clarifying what the returned identity data contains across credential types.

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 uses a specific verb ('Return') and a clear resource ('who this MCP credential acts as'), then enumerates exact output fields: principal email/role, agent name, client install, and last-used time. This clearly distinguishes it from sibling auth_revoke_self, which is a destructive credential operation.

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 states the tool works for both br_ik_* instance keys and br_oat_* OAuth tokens, and explains how OAuth-specific fields behave under instance keys. It gives clear context for when to call it, though it does not explicitly name alternatives or exclusions.

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