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

Goes well beyond the annotations (which only cover read-only/idempotency safety) by disclosing token lifetime semantics (default 1 year, configurable via token_ttl_days), session-scoped reuse, the 401 invalid-credentials failure mode, and the register_account-has-no-password gotcha. No contradictions with the annotation set.

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 the core action and return value, then caveats. Slightly dense and mildly redundant (the 'register_account accounts have no password' point is stated twice), but every sentence carries actionable information.

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 still tells the agent what comes back (the token) and how long it lasts, and it covers the main error and the account-state prerequisite. Nothing essential to calling this correctly 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 coverage is 100%, so the schema already documents all three parameters; the description still adds value by explaining what token_ttl_days controls (the token's usable lifetime and the 365-day default) and reinforcing the password prerequisite. It stops short of adding format/syntax detail beyond 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 precise verb (log in) and the exact inputs (email + password) plus what it produces (a reusable bearer token). It is clearly distinguishable from siblings like register_account, set_password, and refresh_token, which it references by name.

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 gives the prerequisite (a password must have been set with set_password), the alternative path (keep using your register token), and the fix (call set_password while still authenticated) for accounts created via register_account. The agent knows both when to use this and what to do instead if it can't.

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