cern-opendata-mcp-server

Get CERN Open Data Records

cern_opendata_get_records

Read-onlyIdempotent

Fetch full metadata for 1-20 records in one call, by recid, DOI, CMS dataset path (/Primary/Era/TIER) or documentation slug. Returns the description, run periods, collision and distribution details, related records, a software-environment summary, the license and a ready citation, plus what a record states of its variable dictionary, physics category, pile-up, keywords, and LHCb magnet polarity and stripping. Documentation and news pages include their markdown body in slices of at most 30,000 characters; body_offset with that one id reads on from where a slice stops. Each response holds to 64,000 bytes: records past it are left out whole and listed under deferred, to pass back as ids. File lists are not included; use cern_opendata_list_files. Identifiers that do not resolve come back under missing with guidance; they do not fail the call.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`ids`	Yes	Identifiers to resolve, 1-20: an array, or one comma-separated string. Forms may be mixed; duplicates collapse.
`body_offset`	No	With exactly one documentation or news id: where its body slice starts, in characters (UTF-16 code units), usually the body_next_offset an earlier call returned. 0 (the default) is the body's start and is accepted with any ids; above 0 needs exactly one id.

Output Schema

TableJSON Schema

Name	Required	Description
`error`	No	Present when the call failed. Absent on success.
`notice`	No	Caveats about the returned records: a documentation body with more to read, or records deferred by the response budget, each with the call that continues it.
`missing`	No	Identifiers that resolved to no record; empty when every id resolved.
`records`	No	Resolved records, in the order of their first matching input.
`deferred`	No	Inputs whose records were left out to hold the response to 64,000 bytes, in input order; pass them as ids to fetch those records. Empty when every resolved record is returned.

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 2, 2026

TDQS

A4.4/5.0

Behavior5/5

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

Annotations only cover safety/idempotency, yet the description discloses real operational behavior: a 64,000-byte response cap with overflow records returned whole under 'deferred' to pass back as ids, unresolved identifiers surfaced under 'missing' rather than failing the call, and 30,000-character body slicing with body_offset continuation. This is exactly the context an agent needs to drive the tool in a loop.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Purpose and identifier forms are front-loaded, and every subsequent sentence carries operational payload (slicing, size cap, missing handling). It is dense and readable, though the very long second sentence could be split for scanability.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return-field documentation is not required, yet the description still explains response structure, pagination, truncation and error semantics. For a read-only lookup tool with full schema coverage, nothing an agent needs to invoke it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so both parameters are already fully documented, including the identifier forms and the body_offset constraint. The description reinforces the same details but adds no syntax or edge-case meaning beyond the schema, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (fetch) plus resource (full metadata for records) and enumerates the four identifier forms accepted. It explicitly differentiates itself from the sibling cern_opendata_list_files, so an agent can route correctly without opening schemas.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives an explicit exclusion and alternative ('File lists are not included; use cern_opendata_list_files') and describes the batching limit (1-20 ids). It does not contrast with cern_opendata_search_records, so the when-to-search-vs-when-to-fetch boundary is left implicit.

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

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