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

Beyond the annotations (which only declare it is a non-idempotent write with no destructive/open-world hint), the description discloses the permission gate, tag inheritance, that the new key counts against the parent limit and cannot exceed it, and that the secret is returned only once with an explicit 'store it, never print it' warning. This is exactly the extra context annotations cannot carry.

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?

Front-loads the core action, then layers purpose, prerequisite, inheritance rules, and the secret-handling warning. Every sentence carries information, though the density is high and slightly longer than strictly necessary.

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 mutating tool with no output schema, the description covers the essential return behavior (secret returned once), the authorization requirement, and the limit/tag inheritance constraints an agent must know to call it correctly. Nothing critical is missing.

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 schema already documents all three parameters in detail. The description restates the same fields and constraints (tags inherit, limit cannot exceed parent's) without adding new syntax or semantics beyond what the schema provides, so baseline 3 applies.

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?

States a specific verb and resource ('Create an API key') and enumerates the created fields (label, tags, monthly limit), letting an agent separate it from siblings like list_keys, revoke_key and update_key. The spend-splitting example clarifies what the tool is for without ambiguity.

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?

Gives a clear usage scenario ('one key per sub-agent or per persona so spend splits and caps separately') and a hard prerequisite (requires the can_manage_keys permission). It stops short of naming alternative tools or stating when *not* to use it, so it is strong context rather than full when/when-not routing.

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