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

Annotations already declare readOnlyHint, idempotentHint, and destructive false, and the description goes well beyond them by adding deterministic behavior, offline execution with no HTTP delivery, the fact that a customer-owned TEST secret is used, and the price of 0.03 USDC per bounded job. These are meaningful behavioral facts an agent needs to calibrate expectations. No contradction with annotations.

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?

Two sentences carry the entire message: core purpose, optional verification, offline constraint, and cost. Every clause earns its place and the main action is front-loaded.

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 7 parameters and no output schema, the description explains what the tool does, its boundaries, and its pricing, which is strong. It does not detail the exact return format or criteria for choosing between modes, but enough exists for an agent to select and invoke the tool correctly in most cases.

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 71%, and most critical parameters (test_secret, payload, timestamp, now, supplied_signature) are already described. The description reinforces the purpose of test_secret and payload and the optional verifiation workflow, but it does not clar ify the distinction between mode values or the meaning of tolerance_seconds. Added value is moderate but not substantial.

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?

Description states a specific verb+resource ('Generates deterministic webhook HMAC-SHA256 fixtures') and a second operation ('optionally verifies a supplied signature'), with no ambiguity. It also sets scope ('customer-owned TEST secret and payload') and notes it is offline. No siblings exist, so there is nothing to distinguish from, but the clarity is excellent.

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?

Description gives clear context and an explicit exclusion: 'It is offline and never delivers HTTP requests or validates a live endpoint.' This tells an agent this is for fixture generation/testing and not for live endpoint validation. However, it does not name alternatives or explicitly state 'use this when you need...', so it falls just short of full guidance.

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