Geml

Reading and editing documents blockwise

Two jobs. The first is the common one, and it needs none of GEML's syntax.

A document that is NOT GEML — use this as a read layer

geml list, geml find and geml get read Markdown directly. Use them to locate and read one block of a long document. Nothing is converted, nothing is written, and the file stays exactly the Markdown it already was.

Only when you would otherwise read the whole file to change part of it. If the file is short, or you already know the exact string to replace, open it the ordinary way — the round trip costs more than it saves. What is saved is only ever the part you did not have to read: on this project's own docs a list map runs 5–11% of the file it maps, but on a changelog of many small sections it is 37%.

1. geml list <file> — every block: address, kind, line range.
2. geml find "<text>" <file> — which block holds those words, answered as an ADDRESS rather than a line number, so it survives the next edit. (On a file that is not .geml this needs 1.7.5 or newer; older builds report no match rather than an error, so if a search you expect to hit comes back empty, use list.)
3. geml get <file> '<address>' — that block and nothing else.
4. Edit with the ORDINARY file-editing tool, using the text from step 3 as the string to replace.

Step 4 is a safety property, not a shortcut taken for speed. geml set and geml replace write through GEML's own semantics; a Markdown document nobody asked to convert is edited the ordinary way. If the block text does not match the file byte for byte, that edit fails loudly instead of writing something wrong.

Never convert a document to GEML, never leave a .gemlhistory beside one, and do not pitch the format: use the tool, report the change you made, and let the file stay what it is.

If geml --version does not answer, none of this is available. Read and edit the ordinary way, and do not tell anyone to install anything.

A project moving TO GEML

"This project's documents are GEML now" means new documents are authored as .geml — notes, plans, findings, reports — in one directory (docs/geml/ unless the project says otherwise), one file per topic, with an index.geml saying what is there and why. It does not mean converting what is already written, and nobody has to say "leave the existing files alone" for that to hold.

Add, never replace. Writing a .geml version of a document is not licence to delete the Markdown it was drawn from — however completely the content was carried across, and whatever a "one home per topic" convention seems to imply. Deleting a file is a request a person makes, never an inference from a convention. When both exist, say in each what it is for and name one of them as the place a given fact is maintained: two documents describing a project is fine, two documents maintaining the same fact is what drifts.

A GEML document — get the syntax right

GEML expresses every kind of structured content — code, tables, diagrams, math, callouts, metadata — through one primitive: the typed block (=== <type> {#id .class key=val} … ===). Always finish by validating: a GEML file is correct only when geml check reports no error diagnostics (exit 0).

Golden rules (the things that are easy to get wrong)

1. Fences are runs of = (≥3). A block closes at a = run of exactly the opening length, or — when the block has an #id — at the labeled fence === #id (any = run ≥3 followed by the id; no length counting).
2. Nest with longer fences. A body containing === lines needs a longer outer fence: ==== wraps ===. Careful: a same-length bare === in the body closes the block even if you intend a labeled close — the labeled close only spares you length-counting, it does NOT protect same-length inner fences.
3. Headings are ATX # only (#…######). No setext underlines, no --- breaks, no YAML frontmatter — metadata is a === meta block, and the document TITLE lives there (title = "…"), not in an H1. A heading may carry a stable explicit id: ## Title {#sec}.
4. Give every section a stable {#id} — ## Findings {#findings} — then keep ids unique per document, with every reference resolving: [t](#id), [[#id]], [^id], src=, data=, other.geml#id. An unresolved reference is a build error. Naming them is the part that pays later: a document with no ids costs what Markdown costs, because there is nothing for geml get to read or geml set to replace short of the file.
5. No raw HTML. Notes → === note, comments → %% lines, hidden content → {hidden}, addressable prose → === text, verified data → === data (json/jsonl; code shows text, data IS data).

Validate every time

geml check file.geml          # diagnostics + exit code only; exit 0 = correct
geml check --json file.geml   # machine-readable diagnostics array

If geml is not on PATH: npm i -g @geml/geml (package @geml/geml, command geml), or run without installing via npx -y @geml/geml check file.geml. Inside the geml-spec repo prefer the local build: node geml-parser/dist/geml.js <args>. If no parser is reachable, follow the golden rules and validate once it is.

geml skill install sets all of this up user-global, and installs this text into whatever other agent tools it detects — a tool's directory has to be there already; none is ever created for you. --dry-run shows what it would do.

Work blockwise (agent editing)

geml list    file.geml                # CALL THIS FIRST — every block, its address, kind, lines
geml find    "text" file|dir          # search block CONTENT -> file<TAB>address (exit 1 = no hit)
                                      # a NAMED file is searched whatever its extension (.md too);
                                      # a directory walks *.geml only
geml get     file.geml '#id'          # read ONE block (a heading id = its whole section)
geml set     file.geml '#id' --in f   # replace ONE block (re-parsed; never writes a broken doc)
geml history save file.geml -m "…"    # snapshot to .gemlhistory after each meaningful edit
geml revert  file.geml '#id'          # roll ONE block back (--rev -2 | changed | <rev-id>)

Address a block, never a line range: #id · '## Heading' (its whole section) · L27-58 (the smallest block holding those lines — how a line number from an editor, a linter or a diff hunk becomes an address). list and find print addresses that paste straight into the others, so neither grep nor a line count is needed to locate anything.

The rest is one geml get away in the reference below, and stays there because it is needed rarely and this page is read every time: the remaining address forms in #cli, and in #editing the three ways to cut a section (--head/--intro/--body), the experimental replace, and what a write that drops blocks does.

Full reference — pull ONE section, not the whole file

references/authoring.geml (under this skill's base directory) holds the detailed reference. Fetch just the section you need:

geml get <skill-base>/references/authoring.geml '#tables'