serena-config

name	serena-config
description	Interactively configure Serena language servers in .serena/project.yml
category	executing
model	claude-haiku-4-5-20251001
argument-hint	(no arguments)
disable-model-invocation	false
user-invocable	true

Always obey .docs/guides/mcp-tools.md. Read it now if not already in context.

/serena-config — Configure Serena language servers

Edit .serena/project.yml to configure which language servers Serena loads. Gather context (read current config + auto-detect) before prompting.

CRITICAL ORDERING RULE: Steps A and B (read + detect) MUST run before any AskUserQuestion call. Do not prompt until the summary has been printed.

---

Step A — Read current .serena/project.yml

1. Read .serena/project.yml at the repo root.
2. If the file does not exist, abort with this exact message and stop:

   Run the Serena MCP at least once to generate .serena/project.yml, then re-run /serena-config.

3. Parse the languages field. Accept either form:
   • Singular language: <value> — treat as a one-item list.
   • languages: YAML list — parse all entries. Record the parsed set as CURRENT_LANGUAGES. The write step will normalize to the languages: list form regardless of which form the file currently uses.

Step B — Auto-detect candidate languages

Use Glob (or mcp__serena__find_file) to detect languages present in the repo. Map common file signals to Serena language identifiers (e.g. *.py/pyproject.toml → python, *.ts/*.tsx/*.js/package.json → typescript, *.go/go.mod → go, *.rs/Cargo.toml → rust, *.sh/*.bash → bash, *.md → markdown, *.yml/*.yaml → yaml, *.toml → toml, *.tf → terraform, etc.). Use judgment — the goal is a useful suggestion, not exhaustive matching.

Collect matches into DETECTED_LANGUAGES. Compute SUGGESTED = DETECTED_LANGUAGES − CURRENT_LANGUAGES.

For the full list of valid Serena language identifiers (to avoid writing an unsupported value), see https://oraios.github.io/serena/01-about/020_programming-languages.html or the Language enum in https://github.com/oraios/serena/blob/main/src/solidlsp/ls_config.py.

Print a plain-text summary to the user, e.g.:

Currently configured: bash
Detected in repo but not configured: typescript, markdown, yaml

If SUGGESTED is empty, just print the first line.

Step C — Ask the user what to change

Issue one AskUserQuestion (single-select, multiSelect: false):

Do you want to add or remove any languages?

Offer at least these options:

• Add suggested — only shown when SUGGESTED is non-empty; label it with the suggested languages, e.g. "Add typescript, markdown, yaml".
• Add / remove custom — user will supply a free-text list in the next prompt.
• No changes — abort without writing.

Required languages: markdown, python, typescript, and yaml are always required. They must always be present in FINAL regardless of what the user requests. After computing FINAL, silently union it with {markdown, python, typescript, yaml} before writing. If the user tried to remove one of these four, note it: Note: markdown, python, typescript, yaml are required and cannot be removed.

If the user picks Add suggested, set FINAL = CURRENT_LANGUAGES ∪ SUGGESTED.

If the user picks Add / remove custom, ask ONE follow-up AskUserQuestion with multiSelect: false and an Other free-text affordance, phrased:

List languages to add and/or remove. Prefix removals with - (e.g. go, rust, -bash).

Parse the reply: tokens without - are additions, tokens with - are removals. Compute FINAL = (CURRENT_LANGUAGES ∪ ADDITIONS) − REMOVALS, then union with the required set.

If the user picks No changes, stop without writing.

If FINAL is empty after enforcing required languages (which cannot happen since required set is non-empty), abort.

If any token in FINAL is not a valid Serena identifier (per the linked reference), warn the user and abort rather than writing an unsupported value.

Step D — Confirm and write

1. Show the proposed FINAL list (sorted alphabetically, with required languages clearly marked) and confirm via one final AskUserQuestion (Yes, write the file / No, abort without writing).
2. If confirmed, Edit .serena/project.yml. Use only this exact YAML format for the languages block — no flow-style, no quotes unless the value requires them:

   languages:
     - lang1
     - lang2
   

   • If the file has a singular language: <value> line, replace it with the above block containing FINAL sorted alphabetically.
   • If the file has an existing languages: block (list or []), replace the entire block (key + all list items) with the new sorted list.
   • Preserve everything else in the file byte-for-byte. Validate mentally that the result is valid YAML before writing: each list item on its own line, indented with exactly two spaces, starting with - .
3. Print:

   Updated .serena/project.yml — languages: [a, b, c]
   

4. Remind the user to restart the Serena MCP:

   Run `claude mcp restart serena` (or the equivalent for your Claude Code version) to pick up the new language list.