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

With no annotations provided, the description carries the behavioral burden and discloses the most critical trait: 'The secret is write-only: the response returns only id, name and type.' It also reveals the type-conditioned validation expectations (e.g., 'at least one entry across the two' for API_KEY). It stops short of covering duplicate-name behavior or failure modes, but the key security-relevant behavior is transparent.

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, each earning its place: purpose, type-to-field mapping, and write-only response behavior. The dense second sentence is structured with clear type labels (BASIC, BEARER, API_KEY, OAUTH2_CLIENT_CREDENTIALS) that make the conditional logic scannable despite the length.

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 12 parameters, nested objects, no annotations, and no output schema, the description covers the essentials: purpose, conditional field requirements, response shape, and downstream usage via httpCredentialId/mcpCredentialId. Additional edge-case detail (duplicate names, limits) would be needed for a 5, but this is strong for the tool's complexity.

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 baseline is 3, but the description adds real value by synthesizing the 12 parameters into a type-driven decision matrix (BASIC: username+password, BEARER: token, etc.) and highlighting conditional rules like the at-least-one API_KEY requirement and optional scope/audience. This goes beyond what the per-field schema descriptions provide.

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 opens with a specific verb+resource: 'Store a reusable auth credential that API tests can use to reach a protected endpoint.' This clearly distinguishes the tool from siblings like create_api_test (creates the test) and delete_api_test_credential/list_api_test_credentials (lifecycle operations on existing credentials).

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 establishes clear context: credentials are stored once and reused by API tests to reach protected endpoints, and the returned id plugs into an API test's httpCredentialId or mcpCredentialId. It does not explicitly name alternatives or exclusions, but the sibling set contains no competing credential-creation tool, so the usage context is effectively unambiguous.

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