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

Beyond the annotations (which already declare mutation, destructive and idempotent), the description discloses real behavioral consequences: setting a signature marks its source 'manual' and permanently overrides Gmail auto-import, empty strings clear values, and signature_enabled=false disables without deleting. It does not cover permissions/auth or rate limits, but the permanence and disable-vs-delete distinctions are valuable non-obvious context.

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 purpose is front-loaded in the first clause, and the remaining sentences are dense with parameter-specific rules rather than filler. It is somewhat long and repeats a few schema-stated defaults (e.g. signature_enabled default true), costing it the top score, but nothing is wasted.

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 7-parameter, no-required-params mutation tool with full schema coverage and an output schema, the description covers clearing semantics, derivation, the enable-without-delete path, reply-mode behavior, and the permanent manual override. An agent has everything needed to invoke this correctly without opening the schema.

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 per-field meaning is already documented and a 3 is the baseline. The description adds cross-parameter behavior the schema states only piecemeal: either/both fields accepted with the missing half derived on send, and it spells out the reply-mode enum semantics ('always' signs every reply/forward, 'never' never does) that the schema only partially defines.

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 ("Set or update the email signature for an inbox") and clearly scopes the operation as a write on signature configuration. It is plainly distinct from signature_get, but it never names the sibling or any other tool, so it stops short of explicit differentiation.

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 gives concrete usage context: pass either or both of signature_text/signature_html, use empty strings to clear, set signature_enabled=false to stop appending without deleting, and sender_name can be set alone. It does not state when to prefer this over signature_get or any exclusion/alternative path, so it is clear context without explicit routing.

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