x402_session_start

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It effectively describes key behaviors: the payment mechanism (on-chain payment), session token characteristics (cryptographically signed, non-custodial), session lifetime concept, and the relationship with x402_session_fetch. It could be improved by mentioning error conditions or rate limits.

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 well-structured and efficiently conveys essential information in four sentences. Each sentence adds value: establishing the session, explaining the session-fetch relationship, describing the payment model, and detailing the token characteristics. There's no wasted text.

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 tool with 9 parameters, no annotations, and no output schema, the description provides good context about the tool's purpose, usage patterns, and behavioral characteristics. It explains the return value (session_id) and how to use it. It could be more complete by mentioning error conditions or providing examples of typical use cases.

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?

With 100% schema description coverage, the schema already documents all 9 parameters thoroughly. The description adds some context about the session establishment process but doesn't provide additional parameter-specific semantics beyond what's in the schema. This meets the baseline expectation when schema coverage is complete.

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 the tool's purpose: 'Establish an x402 V2 payment session' with specific details about making a single on-chain payment and receiving a signed session token. It distinguishes from sibling tools like x402_session_fetch by explaining the relationship between them.

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?

The description provides explicit usage guidelines: 'All subsequent calls to the same endpoint within the session lifetime use x402_session_fetch — no additional payments required.' It clearly explains when to use this tool versus its sibling x402_session_fetch, and mentions the 'Agents pay once per session rather than once per API call' principle.

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