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

Annotations declare readOnlyHint=false, destructiveHint=false, idempotentHint=false, openWorldHint=false, so the tool is a mutating, non-idempotent operation. The description adds critical behavioral details: the secret is shown exactly once and the data key is shown exactly once, the account gets no credits of its own (free calls come from daily credit accounts), and the 409 behavior on existing address. These add value beyond annotations, but the description does not fully disclose that the secret must be stored by the owner (it says 'Keep the secret with the owner' – that is guidance, not disclosure of data loss risk). There is no contradiction. Given the annotations already reveal mutation, the description adds useful but not exhaustive behavioral context, so a 3 is fair.

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 relatively dense but packs a lot of essential info. It is front-loaded with the primary action, then details the special outputs (secret, data key), the credit behavior, the configuration usage, and the error case. It could be slightly more concise but every sentence carries necessary information. No redundancy with schema. A 4 is appropriate.

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?

The tool has an output schema, which likely documents the return structure, so the description need not explain return values. Given that, the description covers all essential usage context: credential handling, secret usage, data key usage, credit behavior, and error handling. It is complete for a complex sign-up flow. The only minor gap is a explanation of the 'configure block' format, but that is likely in the output schema. A 4 is justified.

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 describes the 'email' parameter fully (owner's email, account identity, one account per address) and coverage is 100%. The description does not repeat the schema's parameter description but adds contextual meaning: it explains that the email will be the identity and that an existing address gets a 409. This adds value beyond the schema (e.g., the one-account-per-address constraint and the error case). Since schema coverage is high, baseline is 3, and the description adds extra meaning, a 4 is appropriate.

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 clearly states a specific action ('Creates a Forum account') on a specific resource (an email address), and distinguishes the result's unique aspects (secret shown once, data key shown once). It clearly differentiates from siblings by describing what this tool does and what it does not do (grants no credits), which no other sibling description does here.

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?

Explicit when-to-use: needed for account creation for an address. It also provides clear when-not: 'An address that already has an account answers 409 email_exists with next_action login_to_link.' This guides the agent to handle this case and implies alternative action (login). It also explains how to use the returned data (configure block, data_key) and the secret for later calls (account_status, get_topup_link).

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