Fetch Router

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

Annotations already declare readOnlyHint=true and openWorldHint=true. The description adds useful behavioral context beyond that: a 30-day window, real verified fetches as the data source, and no cost or key requirement. It does not describe output shape or latency, but the annotation coverage lowers the burden.

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 tight sentences, front-loaded with what the tool returns and followed by when to use it. Every clause contributes useful information without repetition.

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 simple one-parameter, read-only lookup, the description covers the result type, time window, data source, and cost/auth context. Without an output schema it could say more about response structure, but it is sufficient for correct selection and invocation.

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 100%, and the single domain parameter is documented in the schema with an example. The description mentions 'for a domain' but adds no syntax or format meaning beyond the schema, so the baseline 3 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 states a specific data resource and scope: pass rates per route for a domain over the last 30 days. It implicitly distinguishes itself from fetch_page by framing itself as a pre-fetch reliability check, though it does not explicitly name the sibling.

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 clear usage context: use it to choose mode/max_cost before fetching a hard site. It also notes free access and no key needed. It lacks explicit when-not guidance or a named alternative, but the intended moment of use is clear.

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

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

Annotations only state readOnlyHint and openWorldHint; the description adds substantial context beyond them: automatic route retries including headless browser, block/CAPTCHA/login-wall detection, and success-only billing. It also discloses the failure contract (ok=false plus reason codes like blocked:cloudflare, http_404) and the anti-retry policy. That is exactly the behavioral load the annotations do not carry.

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?

Four tight sentences, front-loaded with the purpose and the success guarantee, then behavior, then cost, then the failure contract. Every sentence carries distinct information and nothing is redundant with the schema.

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 no output schema, the description must explain return semantics, and it does: markdown by default, an ok flag, and a reason string on failure. Combined with cost and retry policy, an agent has everything needed to call it and interpret the result correctly.

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 all five parameters are already documented with defaults, enums and ranges; baseline is 3. The description only restates that markdown is the default return mode and refers vaguely to 'settings', adding no new meaning for max_cost, expect_text or expect_selector.

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?

States a specific verb and resource ('Fetch a public URL') plus the differentiator that content is returned 'only if it really loaded'. An agent can immediately tell this is a verified fetch rather than a blind HTTP GET. It does not explicitly contrast with the sibling domain_reliability, which keeps it from a 5.

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?

Gives clear situational guidance: use it to obtain page content, and if ok is false, do not retry the same URL with the same settings. That is a real exclusion rule with an example error taxonomy. It lacks explicit routing to/against the sibling domain_reliability tool, so it stops short of 5.

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