Get payment session

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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered by structured data. The description adds genuine scope context beyond that: the enumerated session contents (including expiry) and the flat statement that 'this server never creates or updates sessions,' which prevents an agent from attempting mutation calls. It omits auth needs, rate limits, and behavior for expired/unknown session IDs.

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 the verb, resource, and lookup key before the returned fields and use case. The closing 'This server never creates or updates sessions' largely restates readOnlyHint and is the one clause that doesn't fully earn its place, but overall there is no filler.

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 one-parameter read tool with no output schema, the description usefully enumerates what comes back, so the agent knows what it can inspect without a response schema. The remaining gaps are minor: session_id format/derivation and the outcome when a session has expired or does not exist.

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 0%, so the description must compensate for a single required string parameter, and it only restates the identifier ('by session_id') without format, origin, or where to obtain the value. It confirms which entity the ID identifies (a Klarna Payments session), which is marginally useful, but adds little semantic detail beyond the property name.

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 (read) and resource (Klarna Payments session) keyed by session_id, then enumerates the payload surface: status, order amount and lines, country/currency, payment method categories, expiry. This is plainly distinct from the sibling set (disputes, orders, captures, payouts, transactions), so an agent can route without opening a schema.

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 a concrete trigger scenario: 'Useful when debugging a checkout that never became an order,' which tells the agent this is a pre-order artifact lookup. It does not name an explicit alternative (e.g., use get_order once a purchase order exists) or state when-not-to-use, so it stops short of full routing guidance.

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