Read Private Message

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

Annotations already provide readOnlyHint=true, so the read-only nature is covered. The description adds value by disclosing the raw post format and, more importantly, the error behavior when the topic is not a PM—information not present in the annotations or schema.

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 a single, front-loaded sentence that immediately states the action and resource, then adds the critical error condition. Every word earns its place, and there is no redundant 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 simple read tool with three well-documented parameters and a readOnlyHint annotation, the description covers the key behavioral context: what is read, in what form, and when it fails. There is no output schema, but 'posts (raw)' gives a reasonable expectation of the return content, and the pagination-related parameters are already documented in the schema.

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%, with each parameter already explained (topic_id, post_limit, start_post_number). The description does not need to add parameter-level detail; it complements the schema by tying topic_id to the PM-topic concept, but adds no meaning beyond what the schema already provides.

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 verb ('Read') and a specific resource ('a private-message topic's posts (raw)'), which clearly differentiates this from reading a regular topic or a single post. It also adds a precise error condition ('Errors if the topic is not a PM'), making the tool's scope unambiguous.

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 gives clear context for when to use the tool: reading the posts of a private-message topic. The explicit error condition 'Errors if the topic is not a PM' acts as an exclusion, signaling the agent not to use this tool for non-PM topics, though it does not name the alternative like discourse_read_topic.

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