# Kroki > Kroki is an open-source HTTP server from Yuzu tech that converts diagram text in 29 formats, including PlantUML, Mermaid, GraphViz and D2, into SVG, PNG or PDF. Owners run it from Docker images, and kroki.io is a free public instance. - Canonical: https://www.anchorterminal.com/tools/kroki - Markdown: https://www.anchorterminal.com/tools/kroki.md (~6,500 tokens) - Slim: https://www.anchorterminal.com/tools/kroki.min.md (~1,730 tokens, same facts, less prose, for token-sensitive contexts) - JSON: https://www.anchorterminal.com/tools/kroki.json (this page as data, same URL with Accept: application/json) - Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt) - API: https://www.anchorterminal.com/api/v1/index.json - Updated: 2026-10-09 ## Overview **Grade C · 59.2/100 · rank #558 of 950 · #8 in Diagramming · not agent-ready · confidence medium** ## Assessment One unauthenticated POST with diagram text returns an image for 29 diagram types, and five versions shipped between 15 July and 5 October 2026. Four advisories were published in July and August 2026, one an unauthenticated remote code execution on `/tikz/svg`, all fixed. No OpenAPI file exists, and the public instance has no terms, privacy policy or status page. ## Facts | Field | Value | | --- | --- | | Vendor | Yuzu tech (https://kroki.io) | | Kind | HTTP API | | Category | Diagramming (https://www.anchorterminal.com/categories/diagramming) | | Transport | HTTP | | Auth | None · No account, key or login on the convert endpoints, on a self-hosted server or on the public instance at kroki.io. The server binds all interfaces on port 8000 unless `KROKI_LISTEN` says otherwise. An optional bearer token, `KROKI_COMPANION_REGISTRATION_TOKEN`, protects only the `/services` registration API, which is off by default. | | Pricing | Free (Free · OSS) · Free under the MIT licence, with nothing to buy. The public instance at kroki.io is free and paid for by sponsors, for reasonable, non-commercial use with no uptime guarantee. Third parties sell hosting, which the project says it does not operate. | | x402 | No · No x402, MPP or L402 in the docs or the source (checked 2026-10-09). | | Licence | MIT | | Packages | oci: `yuzutech/kroki`; oci: `yuzutech/kroki-mermaid`; oci: `yuzutech/kroki-bpmn`; oci: `yuzutech/kroki-excalidraw` | | Source | https://github.com/yuzutech/kroki | | Docs | https://docs.kroki.io/kroki/setup/usage/ | | llms.txt | not found | | Last release | 2026-10-05 | | GitHub stars | 4,365 (as of 2026-10-09) | | Surfaces | HTTP API on a self-hosted gateway server (Java, Vert.x) or the public instance at https://kroki.io. A separate Go CLI, `kroki`, calls either | | Requests | `GET ///`, `POST /` with `diagram_source`, `diagram_type`, `output_format` and optional `diagram_options`, or `POST /` and `POST //` with a plain text or JSON body | | Diagram types | 29 on the home page. ActDiag, BlockDiag, BPMN, Bytefield, C4 with PlantUML, D2, DBML, Ditaa, Erd, Excalidraw, GoAT, GraphViz, Mermaid, Nomnoml, NwDiag, PacketDiag, Pikchr, PlantUML, RackDiag, SeqDiag, Structurizr, Svgbob, Symbolator, TikZ, UMlet, Vega, Vega-Lite, WaveDrom and WireViz. diagrams.net is experimental | | Export formats | SVG for every type. PNG for 18, PDF for 14, JPEG for four, and `txt` and `base64` for PlantUML, C4 and Structurizr, per the home page table | | Containers | `yuzutech/kroki` is the gateway with 25 endpoints built in. Mermaid, BPMN, Excalidraw and diagrams.net run in companion containers `yuzutech/kroki-mermaid`, `-bpmn`, `-excalidraw` and `-diagramsnet` | | Safe mode | `KROKI_SAFE_MODE` is `SECURE` by default, with `SAFE` and `UNSAFE`. `SECURE` maps PlantUML to its `SANDBOX` profile and Structurizr to restricted mode | | Limits | 5 seconds for a diagram binary, 20 for a Java library, 30 for a companion and 10 for a Mermaid render. URI 4,096 characters, headers 8,192, Mermaid source 50,000 characters and 500 edges. All set by environment variables | | Errors | HTTP status with a body in the format the Accept header asks for, JSON `{"error": {"code", "message"}}`, plain text, HTML or an SVG image of the message (from `ErrorHandler.java`) | | Operations | `GET /health` (also `/v1/health` and `/healthz`) lists library versions, `GET /metrics`, OpenTelemetry tracing by environment variable, and TLS with `KROKI_SSL` | | Public instance | https://kroki.io, free and paid for by sponsors, with no key. No terms, privacy policy, status page or rate limit is published. The CLI page says the demonstration server is for reasonable, non-commercial use with no uptime guarantee | | Capabilities | diagram.as-code, diagram.create, diagram.export, diagram.architecture | | Tags | open-source, self-hosted, http-api, docker, diagram-as-code, plantuml, mermaid, graphviz, no-auth, free | | JSON | https://www.anchorterminal.com/api/v1/tools/kroki.json | ## Score breakdown (methodology v0.4, October 2026 research run) Assessed 2026-10-09 from public evidence against the published checklist (https://www.anchorterminal.com/benchmark/#checklist). Confidence: medium. Performance and Task success pending (no score, not in the total); the total is Σ(score × weight) ÷ 80 over the 7 assessed categories. "This run" is each category's share of the 100 points. | Category | Weight | This run | Score (0–100) | Points | | --- | --- | --- | --- | --- | | Reliability | 16% | 20 | 74 | 14.8 | | Performance | 10% | pending | pending | n/a | | Schema & documentation | 13% | 16.2 | 48 | 7.8 | | Agent ergonomics | 13% | 16.2 | 70 | 11.4 | | Security & auth | 14% | 17.5 | 56 | 9.8 | | Payments & pricing | 10% | 12.5 | 60 | 7.5 | | Task success | 10% | pending | pending | n/a | | Maintenance & community | 7% | 8.8 | 86 | 7.5 | | Transparency & trust (editorial 67, provenance 56) | 7% | 8.8 | 62 | 5.4 | | Negative events | up to −15 | up to −15 | 27 July to 12 August 2026. Four advisories on the repository. GHSA-wmpp-fj9c-w766 (critical, CVSS 9.8) allowed unauthenticated remote code execution on `/tikz/svg` in 0.21.0 up to 0.32.0 whatever the safe mode. GHSA-r54f-fq6c-53vw (high, CVE-2026-102359), GHSA-px99-rjv4-49g8 (medium, CVE-2026-102356) and GHSA-9p7m-vrmg-qp4q (high) let TikZ, Mermaid and Vega diagrams read local files or fetch URLs in `SECURE` mode. All are fixed, in 0.32.1 at the latest, and the maintainers published each with a changelog entry, so the deduction is five points (https://github.com/yuzutech/kroki/security/advisories). | -5 | | **Total** | | | | **59.2 → C** | ### Why each score - Reliability 74: Read with the local-software lines, because the listing grades the server an owner runs. The free public instance has no status page, SLA or published limit. Docker images `yuzutech/kroki` and four companions, plus a standalone jar built for Java 11, with the image on a Java 21 runtime (20). The `main.yaml` workflow passed on the last ten pushes to `main`, the latest on 7 October 2026 (25). GitHub's search counts 136 open issues. Most of the 30 newest are proposals for new diagram types and nearly all have a reply, while a September 2025 report of Mermaid PNG faults under high concurrency has none (17). CHANGELOG.md follows Keep a Changelog and states semantic versioning, and 0.33.0 records its change of the default Mermaid layout under Changed with the option that restores the old one (12). Version 0.33.0, with no 1.0 and no statement of stability, and diagrams.net marked experimental (0). - Performance: Pending. Latency is measured per call by our probes, which haven't run yet, so this run doesn't score it. Its weight is shared across the assessed categories until the first probe window closes. - Schema & documentation 48: No OpenAPI file or other machine-readable contract. `GET /health` returns the diagram types and library versions as JSON (3). No llms.txt on kroki.io or docs.kroki.io (HTTP 404). The docs are AsciiDoc files in the repository (2). The usage page states the four request forms and the order of precedence for options in a few hundred words (12). Three JSON fields, a table of diagram types against output formats, and a diagram options page with allowed values per library (10). Examples for cURL and HTTPie, and encoding samples in ten languages. Status codes 400, 408, 413, 414, 422 and 431 are described where each limit is documented, with no error catalogue, and the JSON error shape is not in the docs (9). A public changelog with dated versions. Paths carry no API version apart from a `/v1/health` alias (12). - Agent ergonomics 70: One request with diagram text in and an image out, and no tool definitions to load. The caller picks the output format, with `txt` and `base64` for PlantUML, C4 and Structurizr only (20). No pagination is needed. Output size is not controllable beyond the format and per-library options such as BlockDiag `size` (12). Errors come back with an HTTP status and a body in the format the Accept header asks for, JSON, text, HTML or an SVG image. This is in `ErrorHandler.java` and not in the docs (12). Rendering is a function of the input, so any call can be retried, and responses carry `Cache-Control: public, max-age=432000` (18). One required field per request. No official SDKs. The Go CLI's newest release is v0.5.0 of December 2022 (8). - Security & auth 56: No credential exists to leak or scope. The server has no authentication on its convert endpoints and binds all interfaces by default, so access control is the owner's network (18). `KROKI_SAFE_MODE` defaults to `SECURE`, which blocks file and network reads by diagram libraries, the container runs as the non-root user `kroki`, and the registration API is off in `SECURE` mode. Four advisories in 2026 showed ways round `SECURE` (13). The server renders the caller's own text and returns an image, with remote includes off by default (9). Request logs, `GET /metrics` and optional OpenTelemetry tracing (6). `SECURITY.md` asks for private GitHub advisories, four advisories were published with fixes in July and August 2026, a Trivy scan of the public images runs nightly and Renovate runs weekly. No security.txt (HTTP 404), bug bounty or certification (10). - Payments & pricing 60: Read with the self-hosted rule. Free software with nothing to buy and no payment protocol (0). No price to publish (20). No card or trial needed (20). An agent can pull the Docker image, or call the public instance, with no signup (20). - Task success: Pending. Task success needs the category task suites run through each tool, which haven't run yet, so this run doesn't score it. Its weight is shared across the assessed categories until then. A data provider's data-quality score is published on its listing now and becomes half of this category when it's scored. - Maintenance & community 86: Version 0.33.0 on 5 October 2026, four days before the check (30). Five versions in the last 90 days, 0.31.1 on 15 July, 0.31.2, 0.32.0, 0.32.1 and 0.33.0 (20). 97 commits since 11 July 2026, replies on nearly all of the 30 newest issues, and each 2026 advisory published within a day of the version that fixed it (20). The public instance reported 0.33.0 four days after the tag. No official SDKs, and the CLI has had no release since December 2022 (7). Renovate batches dependency updates weekly with a seven-day minimum age, CI runs on every push and a CVE scan runs nightly (9). - Transparency & trust 62: MIT licence, with every component in one public repository (30). No privacy policy or terms for the software or for the public instance. The docs call the server stateless and say the public instance makes no remote calls. The kroki.io home page loads a Carbon Ads script (15). `KROKI_PORT` is marked deprecated with the reason and a replacement, and no removal date. Removed behaviour is recorded in the changelog (8). OpenTelemetry tracing is configured by environment variable. The 0.32.0 changelog discloses that the companions' headless Chromium contacted Google hosts at launch and that the calls are now blocked (14). Fix list for a coding agent, everything this grade says the listing lacks, the biggest gain first (22 items): https://www.anchorterminal.com/fixes/kroki.md (JSON https://www.anchorterminal.com/fixes/kroki.json) ### What we couldn't check - No terms or privacy document was found for the software or the public instance, so `provenance.terms` and `provenance.privacy` are left out - The legal form of Yuzu tech. Its site names none, and no company register was searched - What the public instance logs or keeps. Nothing is published, and the listing grades the server an owner runs - Whether OpenTelemetry sends anything when no `OTEL_*` variable is set. `Main.java` initialises the autoconfigured SDK at start and the exporter default was not traced - How many of the 136 open issues are crashes or regressions. Only the 30 newest were read - unchecked: Docker Hub pull counts and image tags. hub.docker.com was not asked - unchecked: whether `https://demo.kroki.io`, the CLI's default endpoint, still answers. It was not called - unchecked: the third-party hosts named in the README (Hostinger, Wovalab, Easypanel, ZopDay), which the project says it does not operate - The gateway reads `KROKI_BODY_LIMIT` in `Server.java`, and the docs name only `KROKI_MAX_BODY_SIZE` for the companions ### Sources - repository, README, CHANGELOG.md, SECURITY.md, licence, docs source, server source, CI workflows and tags (shallow clone): (seen 2026-10-09) - usage page, request forms and options: (seen 2026-10-09) - configuration, safe mode, timeouts and limits (docs source): (seen 2026-10-09) - install page, container images and endpoints (docs source): (seen 2026-10-09) - Kroki CLI page and the demonstration server caution (docs source): (seen 2026-10-09) - changelog, versions and security fixes: (seen 2026-10-09) - four published security advisories: (seen 2026-10-09) - home page, diagram types and formats, sponsors and the free service: (seen 2026-10-09) - health endpoint of the public instance, one request: (seen 2026-10-09) - robots.txt, llms.txt and security.txt checks: (seen 2026-10-09) - repository statistics, CI runs, advisories, open issues and CLI releases: (seen 2026-10-09) - Kroki CLI releases: (seen 2026-10-09) - vendor site: (seen 2026-10-09) - domain registration: (seen 2026-10-09) ## Who's behind it (provenance 56/100, checked 2026-10-09) | Check | Finding | Points | | --- | --- | --- | | Legal entity named | Yuzu tech, a French software firm. No registered legal form found | 20/20 | | Domain age | kroki.io, registered 2019-01-06 (7 years) | 11/15 | | Endpoint on the vendor's domain | kroki.io | 15/15 | | Terms of service | not found | 0/10 | | Privacy policy | not found | 0/10 | | Status page | not found | 0/10 | | Changelog | published | 10/10 | | security.txt | not found | 0/10 | The kroki.io home page says Kroki is built and maintained by Yuzu tech, and links https://yuzutech.fr, whose pages name no legal form or registration number. `LICENSE` reads Copyright (c) 2020-present Kroki No terms or privacy document was found on kroki.io or docs.kroki.io, for the software or for the public instance. The MIT licence stands in for the software https://kroki.io/.well-known/security.txt answered 404 on 9 October 2026. `SECURITY.md` asks for reports through a private GitHub security advisory The lead wrote the vendor as Yuzutech. The site writes Yuzu tech, and the GitHub organisation is `yuzutech` The endpoint on the vendor's domain is the free public instance. The listing grades the server an owner runs ### Terms and privacy, as read A reading by a fixed set of rules, each answered with the vendor's own sentence. Not legal advice. **Terms of service**. We found no terms of service published for this product, so there is nothing to read and the check scores 0. **Privacy policy**. We found no privacy policy published for this product, so there is nothing to read and the check scores 0. ## Live (updated 2026-10-09 18:46 UTC) - github `yuzutech/kroki` v0.33.0, released 2026-10-05 - Watching changelog - Always current: https://www.anchorterminal.com/api/v1/live/kroki.json ## Probe metrics Not measured yet. Our benchmark probes haven't run, so there's no availability, latency or error rate from a run and Performance is pending. Live uptime, where we poll the endpoint, is under Live and doesn't change the score. ## Strengths - `POST /` with `diagram_source`, `diagram_type` and `output_format`, or plain text to `//`, returns the image. No account or key - One API covers 29 diagram types, among them PlantUML, C4, Structurizr, Mermaid, GraphViz, D2, DBML, BPMN, Excalidraw and Vega - `KROKI_SAFE_MODE` defaults to `SECURE`, which blocks file and network reads by diagram libraries, and the container runs as the non-root user `kroki` - Five versions shipped between 15 July and 5 October 2026, and the `main.yaml` workflow passed on the last ten pushes to `main` - MIT licence. The maintainers published four security advisories in 2026, each with a fixed version and a changelog entry ## Weaknesses - GHSA-wmpp-fj9c-w766 (CVSS 9.8) allowed unauthenticated remote code execution on `/tikz/svg` in versions 0.21.0 up to 0.32.0, whatever the safe mode. Fixed 3 August 2026 - Three more advisories in July and August 2026 let TikZ, Mermaid and Vega diagrams read local files or fetch URLs in `SECURE` mode. All are fixed in 0.32.1 - No OpenAPI file, llms.txt or error catalogue. The JSON error shape is in the source and not in the documentation - The public instance at kroki.io has no terms, privacy policy, status page or published rate limit. The CLI page limits the demonstration server to reasonable, non-commercial use - The server has no authentication on its convert endpoints and binds all interfaces on port 8000 by default. The version is 0.33.0, with no 1.0 ## Before you call it (notes for agents) 1. Send `POST //` with `Content-Type: text/plain` and the diagram as the body. This avoids the deflate and base64 encoding that GET needs 2. Send `Accept: application/json` on a JSON request to get errors as `{"error": {"code", "message"}}`. With an SVG Accept header the error arrives as an image 3. Call `GET /health` first to list the diagram types and library versions the instance has. Mermaid, BPMN, Excalidraw and diagrams.net need companion containers 4. Run 0.32.1 or later before rendering untrusted text. Earlier versions allow remote code execution through `/tikz/svg` and file reads in `SECURE` mode 5. Self-host for private diagrams with `docker run -p8000:8000 yuzutech/kroki`, and set `KROKI_LISTEN=127.0.0.1:8000` or a network rule, since the server has no authentication ## Connect Install: ```bash docker run -p8000:8000 yuzutech/kroki ``` First request: ```bash curl https://kroki.io/graphviz/svg --data-raw 'digraph G {Hello->World}' ``` Through letme (picks today, calling later): https://letme.dev/kroki. letme answers with the pick and how to call it direct; calling through letme (one key, the vendor's own price) comes later. How it works: https://www.anchorterminal.com/letme/index.md ## Similar tools Ranked by shared capabilities, then score. Same-category tools with no shared capability key are listed last. | Tool | Grade | Score | Rank | Shared capabilities | x402 | Markdown | | --- | --- | --- | --- | --- | --- | --- | | PlantUML | B | 66.9 | 270 | diagram.as-code, diagram.create, diagram.export, diagram.architecture | no | https://www.anchorterminal.com/tools/plantuml.md | | D2 | B | 65.3 | 322 | diagram.as-code, diagram.create, diagram.export, diagram.architecture | no | https://www.anchorterminal.com/tools/d2.md | | draw.io + MCP | B | 62.2 | 439 | diagram.create, diagram.as-code, diagram.export, diagram.architecture | no | https://www.anchorterminal.com/tools/drawio.md | | Structurizr + MCP | C | 59.9 | 533 | diagram.create, diagram.as-code, diagram.export, diagram.architecture | no | https://www.anchorterminal.com/tools/structurizr.md | | Eraser API + MCP | E | 38.6 | 918 | diagram.create, diagram.as-code, diagram.export, diagram.architecture | no | https://www.anchorterminal.com/tools/eraser.md | | tldraw SDK + MCP | C | 60.7 | 498 | diagram.create, diagram.as-code, diagram.export | no | https://www.anchorterminal.com/tools/tldraw.md | ## Panel reviews (0) Reviewed by the Anchor panel (https://www.anchorterminal.com/reviewers/index.md): . Desk reviews, written from public documentation, pricing, terms, source and status history on 1 October 2026. No calls made. For a desk review, the outcome says whether the reviewer's questions could be answered from public material: success, partial or failure. How reviews work: https://www.anchorterminal.com/reviews/how-it-works.md ## Notable - The API takes GET with the diagram deflated and base64-encoded in the path, `POST /` with JSON, or `POST //` with plain text. Options go in `diagram_options`, `Kroki-Diagram-Options-*` headers or query parameters (source: ) - GHSA-wmpp-fj9c-w766, published 3 August 2026 with CVSS 9.8, allowed unauthenticated remote code execution on `/tikz/svg` in 0.21.0 up to 0.32.0, whatever `KROKI_SAFE_MODE` was set to (source: ) - Version 0.32.0 of 3 August 2026 stopped the headless Chromium in four companion containers from contacting five Google hosts at launch. The changelog says a packet capture confirmed the calls (source: ) - Version 0.33.0 of 5 October 2026 made ELK the default Mermaid layout, with `layout=dagre` to restore the old one (source: ) - `https://kroki.io/health` reported Kroki 0.33.0, D2 0.7.1, Mermaid 12.1.0 and PlantUML 1.2026.8 on 9 October 2026 (source: ) - The Kroki CLI's newest release is v0.5.0 of 8 December 2022, and the docs page for it shows version 0.1.0 (source: ) - #9 of 15 in Best diagramming APIs and diagram-as-code for AI agents: https://www.anchorterminal.com/best/diagramming/index.md - All 99 diagrams comparisons: https://www.anchorterminal.com/compare/diagramming/index.md ## Compare - [Cloudviz API vs Kroki](https://www.anchorterminal.com/compare/cloudviz-vs-kroki.md): F 37.7 vs C 59.2 - [Diagrams.so API + MCP vs Kroki](https://www.anchorterminal.com/compare/diagrams-so-vs-kroki.md): C 60 vs C 59.2 - [draw.io + MCP vs Kroki](https://www.anchorterminal.com/compare/drawio-vs-kroki.md): B 62.2 vs C 59.2 - [Eraser API + MCP vs Kroki](https://www.anchorterminal.com/compare/eraser-vs-kroki.md): E 38.6 vs C 59.2 - [Excalidraw vs Kroki](https://www.anchorterminal.com/compare/excalidraw-vs-kroki.md): C 54.5 vs C 59.2 - [Kroki vs Mural MCP](https://www.anchorterminal.com/compare/kroki-vs-mural-mcp.md): C 59.2 vs E 41.9 - [Kroki vs Whimsical MCP](https://www.anchorterminal.com/compare/kroki-vs-whimsical.md): C 59.2 vs D 52.6 - [D2 vs Kroki](https://www.anchorterminal.com/compare/d2-vs-kroki.md): B 65.3 vs C 59.2 - [Kroki vs Lucid API + MCP](https://www.anchorterminal.com/compare/kroki-vs-lucid.md): C 59.2 vs C 60.6 - [Kroki vs Mermaid Chart MCP](https://www.anchorterminal.com/compare/kroki-vs-mermaid-chart.md): C 59.2 vs F 31.4 - [Kroki vs PlantUML](https://www.anchorterminal.com/compare/kroki-vs-plantuml.md): C 59.2 vs B 66.9 - [Kroki vs Structurizr + MCP](https://www.anchorterminal.com/compare/kroki-vs-structurizr.md): C 59.2 vs C 59.9 - [Kroki vs tldraw SDK + MCP](https://www.anchorterminal.com/compare/kroki-vs-tldraw.md): C 59.2 vs C 60.7 ## Verify this listing For the vendor. The badge or a plain link to this page verifies the listing, from a page on kroki.io or one of its subdomains, or the README of github.com/yuzutech/kroki. It shows the listing is the vendor's and that the vendor knows it's here, and it never changes a grade, rank or review. The vendor sends the page's address to `POST https://www.anchorterminal.com/api/v1/verify` as `{"slug": "kroki", "url": "…"}`, or calls the `verify_listing` tool at https://www.anchorterminal.com/mcp. We fetch the page once, then again every week; two failed checks in a row and the verification lapses, and a later pass restores it. What we check: https://www.anchorterminal.com/builders/index.md#verify HTML badge: ```html Kroki on Anchor Terminal ``` Markdown badge, for a README: ```markdown [![Kroki on Anchor Terminal](https://www.anchorterminal.com/badges/kroki.svg)](https://www.anchorterminal.com/tools/kroki) ``` Plain link: ```html Kroki on Anchor Terminal ``` ## Share this listing For the vendor. Sharing assets for social media, two PNGs of 1200 × 630 that say Kroki is listed on Anchor Terminal, with the vendor's logo and this page's address and no grade or score. - Dark: https://www.anchorterminal.com/assets/share/kroki-dark.png - Light: https://www.anchorterminal.com/assets/share/kroki-light.png