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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, and the description still adds substantive context beyond them: nothing is joined until the person opens the link, no account is ever created server-side, and the caller must share the link rather than open it. It also discloses the Weekly Relay placement rule ('placed on an open team with room') and the two-URL return shape.

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?

It is front-loaded with the purpose and then the usage rule, and every sentence carries information (mode selection, side effects, sharing instruction, return shape). The mode-selection sentence is a long colon-and-parenthetical run-on that could be split for faster scanning, which keeps it just short of top marks.

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 zero-required-parameter tool with three distinct invocation modes, the description covers the mode selection, the side-effect boundary, caller obligations and even which URL is returned for new versus existing users. With an output schema present, nothing further about return values is needed.

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 the schema already documents the three parameters, which sets a baseline of 3. The description earns above that by adding conditional logic the schema does not express: invite_code only matters for private challenges, an outpace.fit/i/ invite link already carries its invite, and omitting both parameters yields a plain sign-up link.

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 concrete verb and resource: 'Get outpace.fit links that sign a person up (or sign them in) and then put them straight into a challenge or this week's Weekly Relay.' That scope clearly separates it from siblings like get_challenge, find_public_challenges and relay_info, which read or inspect rather than produce a join link.

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 states exactly when to use it ('whenever the person wants to join an OutPace challenge or the Weekly Relay, or to sign up for OutPace') and explicitly names the alternatives it replaces: pointing to a web search result or the app store. It also maps each mode (share_code, weekly_relay, neither) to a distinct situation, so no inference is required.

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