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

Beyond the annotations it discloses the return payload (known vector, match result, draft source SHA), the no-credentials constraint, and a per-call cost of 1 MESH, which is genuine added context. However readOnlyHint=false sits a little awkwardly against a description that portrays a pure computation, and the description does not address whether the call has any side effects; the mismatch is not severe enough to call a contradiction.

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 core sentence is front-loaded and useful, but the string is padded with bracketed metadata ('[unverified]', '(1 MESH/call, a tool · developer-tools)') and slightly redundant framing ('Isolated proof demonstrator' then 'This is a small test endpoint'). It remains readable, just not tight.

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 one-parameter tool with no output schema, the description covers what to send, what not to send, what comes back (vector, match result, source SHA), and the limits of the guarantee. Nothing an agent needs in order to call it correctly is missing, aside from any note on side effects implied by readOnlyHint=false.

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% and there is only one parameter, so the baseline is 3. That baseline is warranted here because the schema's own description is generic boilerplate about agent-brain/agent-memory payloads rather than this tool; the description partially compensates by stating 'Send an empty JSON object', which is the only reliable guidance about what 'input' should contain.

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 names a concrete verb and object ('computes the public RFC7636 Appendix B S256 challenge') and frames the tool as an isolated proof/test vector, which separates it from general-purpose siblings like agent-brain or code-review. The header phrase 'Isolated proof demonstrator' plus the explicit 'not a production OAuth assurance' line makes the scope unmistakable, though the trailing '[unverified]' token muddies an otherwise crisp statement.

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 tells the agent exactly how to invoke it ('Send an empty JSON object') and what not to expect ('Accepts no real verifiers or credentials'), and warns it is a test endpoint rather than a production assurance tool. It never names an alternative for real PKCE verification work, so the when-to-use vs. siblings is only implied by the word 'test'.

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