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Basecamp MCP Server

by stefanoverna
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Remote

Update Basecamp Message

basecamp_update_message

Update a Basecamp message's subject, body, or type. Apply partial content edits like append, prepend, or find-and-replace to avoid rewriting the entire post.

Instructions

Update a message. Use partial content operations when possible to save on token usage.

HTML rules for content:

  • Allowed tags: p, span, h2, h3, h4, br, strong, em, strike, code, a (with href attribute), pre, ol, ul, li, blockquote, mark, figure, figcaption, table, tbody, tr, th, td, div, bc-attachment.

  • Wrap every paragraph in ..., and put between one paragraph and the next. Both parts are necessary: newlines and blank lines in your HTML are discarded, and Basecamp shows no space around a on its own, so two paragraphs with nothing between them are shown as one block of text. Do not rely on line breaks in your HTML to separate paragraphs.

  • Headings: use , , as appropriate.

  • Inline code: text. Preformatted blocks: text.

  • Ordered lists: .... Unordered: ....

  • Tables: Heading...Cell...

  • To mention a person: . Put the tag where the name must show in the text, for example "Thanks for the fix". The person gets a notification. If the ID is not a person, the tool returns an error and writes nothing. Get person IDs from basecamp_list_people, or from the people in other responses (assignees, creators).

  • Single image:

  • Image gallery: wrap multiple in a .

  • A bc-attachment needs an attachable_sgid. For a file that is already in Basecamp, take the sgid from the HTML content of the message, comment or card that shows it, or use basecamp_list_recordings. For a file that is not in Basecamp yet, such as an image at an external URL or a screenshot on disk, upload it with basecamp_create_attachment and use the sgid that it returns. There is no tag, so an external image URL can never be embedded directly: upload it, or accept that it stays a plain link.

  • Basecamp auto-enriches bc-attachment tags after saving (adds url, href, filename, content-type, etc.) — you never need to write those.

  • When you see an existing, already-enriched tag (e.g. from a previous list/get call), leave its inner HTML alone. Before any content_append/content_prepend/search_replace runs, it is automatically collapsed back to its minimal form (sgid, presentation, caption, and content-type for mentions) — you don't need to strip it yourself, and doing so manually is unnecessary and risks mismatched find strings.

  • Background highlights: ...

  • Text color highlights: ...

  • For both, N is 1 (yellow), 2 (amber), 3 (red), 4 (pink), 5 (purple), 6 (blue), 7 (teal), 8 (near-white), or 9 (light gray).

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
contentNoIf provided, replaces entire HTML content. Cannot be used with content_append, content_prepend, or search_replace.
subjectNoNew message subject
message_idYesBasecamp resource identifier
content_appendNoText to append to the end of current content. Cannot be used with content.
search_replaceNoArray of search-replace operations to apply to current content. Cannot be used with content.
content_prependNoText to prepend to the beginning of current content. Cannot be used with content.
message_type_idNoOptional message type/category ID

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed6 schema fields changedv1.2.1
    • removedInput schema / properties / bucket_id
      Removed value: -{
-  "description": "Basecamp resource identifier",
-  "type": "number"
-}
    • removedInput schema / properties / message_id / $ref
      Removed value: -"#/properties/bucket_id"
    • addedInput schema / properties / message_id / description
      Added value: +"Basecamp resource identifier"
    • addedInput schema / properties / message_id / type
      Added value: +"number"
    • changedInput schema / properties / message_type_id / $ref
      Previous value: -"#/properties/bucket_id"New value: +"#/properties/message_id"
    • changedInput schema / required
      Previous value: -[
-  "bucket_id",
-  "message_id"
-]New value: +[
+  "message_id"
+]
  2. Addedv1.0.0

TDQS

A4.1/5.0
Behavior5/5

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

Beyond the annotations, the description discloses rich behavioral detail: HTML tag restrictions, paragraph handling, mention-side effects (notification, error-and-no-write on invalid person IDs), attachment auto-enrichment, automatic collapsing of enriched bc-attachment tags before partial operations, and the absence of an <img> tag. This is exactly the kind of context an agent needs before mutating message content.

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?

The description is long, but it is front-loaded with the core operation and then organized into a clearly labelled HTML-rules bullet list. Most rules earn their place for an agent writing Basecamp-compatible HTML, though the volume of formatting detail makes it less concise than an ideal tool description.

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?

For a complex mutation tool with seven parameters, 100% schema coverage, no output schema, and annotations that only cover safety hints, the description completes the missing operational picture. It covers content editing modes, HTML formatting, mentions, attachments, error behavior, and automatic normalization, leaving no major agent-facing gap.

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

Parameters4/5

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

Schema coverage is 100%, so the baseline is 3. The description adds meaningful semantics for the content-related parameters by explaining allowable HTML, the need for <p> wrapping, attachment sgid sourcing, and mention syntax. It does not add much beyond the schema for subject, message_id, or message_type_id, so it lands above baseline but not at the top.

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

Purpose4/5

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

The description opens with a specific verb and resource: 'Update a message.' An agent can identify this as the message-update operation. However, it does not explicitly distinguish this tool from siblings like basecamp_update_comment or basecamp_update_document, so sibling differentiation is left to the resource name.

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

Usage Guidelines3/5

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

The description advises using partial content operations to save tokens, which is useful guidance for choosing among content/content_append/content_prepend/search_replace. It does not say when to use this tool versus basecamp_create_message or basecamp_update_comment, nor does it mention prerequisites such as needing the message_id or permission context.

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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