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

Annotations only declare the mutation safety profile (readOnly=false, idempotent=false); the description adds the real behavioral context an agent needs — state survives across scrapes, the engine is pinned for the session's lifetime and cannot change, the default engine resolution order (obscura → chromium → fetch), and the fields returned. This is substantive disclosure beyond structured fields.

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?

Front-loaded with purpose and usage, then defaults, release, and return shape. It is long but each sentence carries information; the closing field enumeration ('id, engine, status, sticky_key, proxy, expires_at') is slightly redundant padding since no output schema exists but the list is still useful.

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 10-parameter, no-required-param, no-output-schema creation tool, the description covers purpose, sibling routing (scrape, release), engine-pinning semantics, defaults, and a field-level summary of the return value. Nothing essential for correct invocation is missing.

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 schema already flags the 'coming soon' parameters, so the baseline is 3. The description still adds value by explaining the engine default-selection fallback logic and the sticky exit IP default, though it does not go deeper into the remaining parameters (ttl_seconds, domain_scores, session_context) than the schema.

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 ('Create a session') and immediately defines what a session is (persistent browser identity: cookie jar, localStorage, pinned engine, sticky exit IP), which cleanly separates it from sibling read/lifecycle tools like spicrawl_session_get or spicrawl_session_context.

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?

Explicitly states when to use it ('multi-step flows — log in, then fetch pages behind the login'), how to consume it ('passing the returned id as session_id to every spicrawl_scrape call that should share state'), and how to end it ('Release the session with spicrawl_session_release'). Alternatives and lifecycle are named, not inferred.

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