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

The description goes far beyond the basic readOnly/destructive hints by disclosing critical behaviors: the secret is sealed at write time and never returned, destinationHost is permanent, and the credential is only sent to that host over https. These are essential constraints not apparent from annotations or schema 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?

The description is dense but every sentence earns its place. It front-loads the main purpose, then methodically covers security, usage pattern, auth type mappings, and destinationHost constraints without redundancy or 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?

With no output schema, the description covers the most important outcome (the secret is not returned, and the credential is referenced by id), but it does not explicitly state what the response contains (e.g., the credential id or a success indicator). This is a minor gap given the strong behavioral context provided.

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?

Although the schema covers every parameter, the description adds crucial cross-field semantics by mapping each auth.type value to the applicable fields (bearer→token, basic→username+password, etc.). It also explains destinationHost's permanence and wildcard matching, which is not obvious from the schema alone.

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 'Save a new reusable credential', which is a specific verb-resource pair and clearly distinguishes this from related tools like create_api_key. It further specifies the credential is sealed with the project's encryption key and references how it is used (by target id), making the purpose unmistakable.

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?

It provides clear usage context by explaining that the secret is never returned and should be referenced from a target via credentialVaultEntryId, pointing to create_endpoint/update_endpoint. It lacks explicit 'when not to use' or alternatives like create_api_key, but the guidance is sufficient for most agents.

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